BUG: Fix concat series loss of timezone

Author: jakezimmer

pandas/core/dtypes/concat.py

@@ -193,7 +193,8 @@ def _concat_categorical(to_concat, axis=0):
 
     def _concat_asobject(to_concat):
         to_concat = [x.get_values() if is_categorical_dtype(x.dtype)
-                     else np.asarray(x).ravel() for x in to_concat]
+                     else np.asarray(x).ravel() if not is_datetimetz(x)
+                     else np.asarray(x.astype(object)) for x in to_concat]
         res = _concat_compat(to_concat)
         if axis == 1:
             return res.reshape(1, len(res))