Update requirements-dev.in to follow branch v12.0 instead of master

Change-Id: I93947235aedb4f6c48917d4c84feedb900b5dfe9
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/requirements-dev.in b/requirements-dev.in
index 279709a..de0a661 100644
--- a/requirements-dev.in
+++ b/requirements-dev.in
@@ -12,5 +12,5 @@
 #     See the License for the specific language governing permissions and
 #     limitations under the License.
 
-git+https://osm.etsi.org/gerrit/osm/common.git@master#egg=osm-common
--r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=master
+git+https://osm.etsi.org/gerrit/osm/common.git@v12.0#egg=osm-common
+-r https://osm.etsi.org/gitweb/?p=osm/common.git;a=blob_plain;f=requirements.txt;hb=v12.0