COMPAT: warnings on scalar comparisons
https://travis-ci.org/pandas-dev/pandas/jobs/410445444

I think these are new in numpy 1.15

```
pandas/tests/extension/integer/test_integer.py::TestDtype::()::test_check_dtype[UInt64Dtype]
  /home/travis/build/pandas-dev/pandas/pandas/core/ops.py:1235: DeprecationWarning: Numeric-style type codes are deprecated and will result in an error in the future.
    result = libops.scalar_compare(x, y, op)
  /home/travis/build/pandas-dev/pandas/pandas/core/ops.py:1235: DeprecationWarning: Numeric-style type codes are deprecated and will result in an error in the future.
    result = libops.scalar_compare(x, y, op)
```