rename master to main branch

.github/workflows/actions.yml

@@ -1,9 +1,9 @@
 name: CI
 on:
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
@@ -27,7 +27,7 @@ jobs:
       - run: cd js/examples && mkdir ../../app/dist/examples && cp *.html ../../app/dist/examples/
       - name: build_app
         uses: peaceiris/actions-gh-pages@v3
-        if: ${{ github.ref == 'refs/heads/master' }}
+        if: ${{ github.ref == 'refs/heads/main' }}
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./app/dist