Add tz-aware change back to changelog.

Author: tswast

docs/source/changelog.rst

@@ -29,11 +29,14 @@ Internal changes
 
 Enhancements
 ~~~~~~~~~~~~
+
 - Allow ``table_schema`` in :func:`to_gbq` to contain only a subset of columns,
   with the rest being populated using the DataFrame dtypes (:issue:`218`)
   (contributed by @johnpaton)
 - Read ``project_id`` in :func:`to_gbq` from provided ``credentials`` if
   available (contributed by @daureg)
+- ``read_gbq`` uses the timezone-aware ``DatetimeTZDtype(unit='ns',
+  tz='UTC')`` dtype for BigQuery ``TIMESTAMP`` columns. (:issue:`269`)
 
 .. _changelog-0.9.0: