change the master/default branch to mitaka

Change-Id: I8589dd92704df9d26d7f9359477c99377223d897

openstack_releases/defaults.py

@@ -12,4 +12,4 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-RELEASE = 'liberty'
+RELEASE = 'mitaka'

tools/tag_history_from_git.py

@@ -43,6 +43,7 @@ RELEASES = [
     ('juno', datetime.datetime(2014, 10, 16)),
     ('kilo', datetime.datetime(2015, 4, 30)),
     ('liberty', datetime.datetime(2015, 10, 15)),
+    ('mitaka', datetime.datetime(2016, 4, 7)),
 ]