COMPAT: recent numpy deprecation warnings
getting lots of deprecation warnings from numpy.

```
(pandas) bash-3.2$ pytest pandas/tests/test_resample.py pandas/tests/io/json/test_json_table_schema.py 
============================================================================================================ test session starts ============================================================================================================
platform darwin -- Python 3.6.3, pytest-3.3.0, py-1.5.2, pluggy-0.6.0
rootdir: /Users/jreback/pandas, inifile: setup.cfg
plugins: xdist-1.20.1, forked-0.2, cov-2.5.1, hypothesis-3.38.5
collected 350 items                                                                                                                                                                                                                         

pandas/tests/test_resample.py ...................................................................................................................ssss................................................................................ [ 56%]
...............................ssss..................................                                                                                                                                                                 [ 76%]
pandas/tests/io/json/test_json_table_schema.py ...................................................x..x..x..x..xxxx..x..x..X..X...                                                                                                     [100%]

============================================================================================================= warnings summary ==============================================================================================================
pandas/tests/io/json/test_json_table_schema.py::TestTableOrientReader::()::test_read_json_table_orient[vals2-None]
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)

pandas/tests/io/json/test_json_table_schema.py::TestTableOrientReader::()::test_read_json_table_orient[vals2-idx]
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)

pandas/tests/io/json/test_json_table_schema.py::TestTableOrientReader::()::test_read_json_table_orient[vals2-index]
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)

pandas/tests/io/json/test_json_table_schema.py::TestTableOrientReader::()::test_comprehensive
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)
  /Users/jreback/pandas/pandas/core/dtypes/cast.py:706: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
    return arr.astype(dtype)

-- Docs: http://doc.pytest.org/en/latest/warnings.html
================================================================================ 330 passed, 8 skipped, 10 xfailed, 2 xpassed, 16 warnings in 12.85 seconds =================================================================================
```


```
In [1]: arr = np.array(['2016-01-01T00:00:00.000Z', '2016-01-02T00:00:00.000Z',
   ...:        '2016-01-03T00:00:00.000Z', '2016-01-04T00:00:00.000Z'], dtype=object)
   ...: 

In [2]: arr.astype('<M8[ns]')
/Users/jreback/miniconda3/envs/pandas/bin/ipython:1: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
  #!/Users/jreback/miniconda3/envs/pandas/bin/python
Out[2]: 
array(['2016-01-01T00:00:00.000000000', '2016-01-02T00:00:00.000000000',
       '2016-01-03T00:00:00.000000000', '2016-01-04T00:00:00.000000000'], dtype='datetime64[ns]')
```

I haven't seen these before, so a recent change must have triggered