Update redoc.yaml

Implement workflow change idea from #28

Author: chatelao

.github/workflows/redoc.yaml

@@ -1,7 +1,13 @@
 name: Node CI
 
 # https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions
-on: [push]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
   build_and_test: