fix(mergify): merge if either push or pr build passes.

.mergify.yml

@@ -1,8 +1,25 @@
 pull_request_rules:
-  - name: automatic merge on CI success and review
+  - name: automatic merge on CI success and review - pr
     conditions:
       - status-success=continuous-integration/travis-ci/pr
+      - status-success=continuous-integration/appveyor/pr
+      - "#changes-requested-reviews-by=0"
+      - base=master
+      - label=ready-to-merge
+      - approved-reviews-by=@leanprover-community/mathlib-maintainers
+    actions:
+     delete_head_branch: {}
+     merge:
+        method: squash
+        strict: smart
+        strict_method: merge
+ # second condition necessary, as mergify was failing if the travis "pr" build
+ # finished before the travis "push" build due to branch protection setting requiring
+ # the "push" build to complete before a merge
+   - name: automatic merge on CI success and review - pr
+    conditions:
       - status-success=continuous-integration/travis-ci/push
+      - status-success=continuous-integration/travis-ci/pr
       - status-success=continuous-integration/appveyor/pr
       - "#changes-requested-reviews-by=0"
       - base=master
@@ -14,6 +31,7 @@ pull_request_rules:
         method: squash
         strict: smart
         strict_method: merge
+
   - name: remove outdated reviews
     conditions:
       - base=master