Corrections from @jreback comments

* Added test for is_timedelta64_dtype
* Added double backticks in what's new

Author: Jean-Mathieu Deschenes

pandas/tests/dtypes/test_common.py

@@ -200,7 +200,7 @@ def test_is_datetime64tz_dtype():
 def test_is_timedelta64_dtype():
     assert not com.is_timedelta64_dtype(object)
     assert not com.is_timedelta64_dtype([1, 2, 3])
-
+    assert not com.is_timedelta64_dtype(np.array([], dtype=np.datetime64))
     assert com.is_timedelta64_dtype(np.timedelta64)
     assert com.is_timedelta64_dtype(pd.Series([], dtype="timedelta64[ns]"))