Fix mergify rules (#241)

Author: christophfroehlich

.github/mergify.yml

@@ -17,9 +17,9 @@ pull_request_rules:
         comment:
           message: This pull request is in conflict. Could you fix it @bmagyar @destogl @christophfroehlich @saikishor?
 
-  - name: development targets master branch
+  - name: development targets ros2-master branch
     conditions:
-      - base!=master
+      - base!=ros2-master
       - author!=bmagyar
       - author!=destogl
       - author!=christophfroehlich
@@ -29,6 +29,6 @@ pull_request_rules:
     actions:
         comment:
           message: |
-            @{{author}}, all pull requests must be targeted towards the `master` development branch.
-            Once merged into `master`, it is possible to backport to `{{base}}`, but it must be in `master`
+            @{{author}}, all pull requests must be targeted towards the `ros2-master` development branch.
+            Once merged into `ros2-master`, it is possible to backport to `{{base}}`, but it must be in `ros2-master`
             to have these changes reflected into new distributions.