Handle FutureWarning from NumPy in Series Construction
This is with NumPy dev.

```python
In [2]: pd.Series(['0', '1'], dtype=float)
/Users/taugspurger/sandbox/numpy/numpy/core/numeric.py:2468: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  return bool(asarray(a1 == a2).all())
Out[2]:
0    0.0
1    1.0
dtype: float64

```

https://travis-ci.org/pandas-dev/pandas/jobs/427640030#L5344

this goes from `core.series._sanitize_array` -> `_try_cast` -> `maybe_cast_to_integer_array`.