Automate PR merging

Author: Antonio Alonso Dominguez

.mergify.yml

@@ -0,0 +1,9 @@
+pull_request_rules:
+  - name: automatic merge when CI passes
+    conditions:
+      - status-success=continuous-integration/travis-ci/pr
+      - base=master
+    actions:
+      merge:
+        method: squash
+      delete_head_branch: {}