build on push to modules branch

.github/workflows/main.yml

@@ -21,7 +21,7 @@ name: Build Docs
 
 on:
   push:
-    branches: [ master ]
+    branches: [ modules ]
   # Initiate a build to pull in the wiki-ui repository changes.
   repository_dispatch:
     types: [wiki-ui-build]
@@ -45,6 +45,7 @@ jobs:
     - name: Clone the repo
       uses: actions/checkout@v2
       with:
+        ref: modules
         # Number of commits to fetch. 0 indicates all history.
         fetch-depth: 1