Merge pull request #12 from yunkon-kim/yunkon-kim-patch-1

Change branch from `master` to `main` in CD workflow

.github/workflows/continuous-delivery.yaml

@@ -13,7 +13,7 @@ on:
   # The "push" event could replace "merged" event.
   push:
     branches:
-      - master
+      - main
     tags:
       # Only trigger on semver shaped tags.
       - "v*.*.*"
@@ -122,4 +122,4 @@ jobs:
           cache-to: type=local,dest=/tmp/.buildx-cache
 
       - name: Image digest
-        run: echo ${{ steps.docker_build.outputs.digest }}
+        run: echo ${{ steps.docker_build.outputs.digest }}