fix bugs in transformer_dla

tensor2tensor/models/__init__.py

@@ -11,4 +11,3 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-

tensor2tensor/models/models.py

@@ -39,4 +39,5 @@ from tensor2tensor.models import transformer_mlrf
 #from tensor2tensor.models import transformer_fix
 from tensor2tensor.models import transformer_relative_pos
 from tensor2tensor.models import transformer_dropout
+from tensor2tensor.models import transformer_dla
 # pylint: enable=unused-import