TST: remove skip for pytables build issue on numpy 1.15

[jreback]

[TomAugspurger]

The root cause is that numpy/numpy#11656

import pickle
import numpy as np
pickle.dumps(np.datetime64('2016-01-01T00:00:00.000000000'))

that just surfaced in the pytables test, since it needs to serialize the datetime64.

[TomAugspurger]

NumPy 1.15.1 is out, and should include this fix.

Updating

pandas/pandas/tests/io/test_pytables.py

Lines 2194 to 2197 in 68273a7

	@pytest.mark.skipif(
	not _np_version_under1p15,
	reason=("pytables conda build package needs build "
	"with numpy 1.15: gh-22098"))

to skip if and only if the NumPy version is exactly 1.15.0 will make for a good first contribution.

[NikhilKumarM]

@TomAugspurger Could you please let me know if I have to make any changes. Thanks!!