Add .mergify.yml configuration

.circleci/config.yml

@@ -2,6 +2,7 @@ version: 2
 workflows:
   version: 2
   workflow:
+    # Keep those job names in sync with .mergify.yml
     jobs:
       - build
       - docs-build

.mergify.yml

@@ -0,0 +1,19 @@
+# See https://doc.mergify.io/configuration.html
+
+pull_request_rules:
+  - name: automerge to master with label automerge
+    conditions:
+      - "#approved-reviews-by>1"
+      - base=master
+      - label=automerge
+      # We need to list them all individually. Here is why: https://doc.mergify.io/conditions.html#validating-all-status-check
+      - "status-success=ci/circleci: build"
+      - "status-success=ci/circleci: coverage"
+      - "status-success=ci/circleci: docs-build"
+      - "status-success=ci/circleci: lint"
+      - "status-success=ci/circleci: test"
+      - "status-success=ci/circleci: test-chrome"
+    actions:
+      merge:
+        method: merge
+        strict: false