use shell as running base, rather than assign docker image

[why] github action doesn't allow ${{ inputs.parameter }} under `image`
[how] revise to use `composite` mode rather than `docker` mode

README.md

@@ -39,7 +39,7 @@ inputs
 * `app-path`: django app folder path. after `action/checkout`, the working dir would be repository root.
   * default: `app`
 * `docker-image`: docker image name. you are able to change the image hub to private source.
-  * default: `docker://hardcoretech/django-migration-checker`
+  * default: `hardcoretech/django-migration-checker`
 * `docker-image-tag` docker image tag, it should represent version of `django-migration-checker` (python package)
   * default: `latest`
 

action.yml

@@ -12,14 +12,20 @@ inputs:
 
   docker-image:
     description: 'docker image name'
-    default: 'docker://hardcoretech/django-migration-checker'
+    default: 'hardcoretech/django-migration-checker'
 
   docker-image-tag:
     description: 'docker image tag of django-migration-checker'
     default: 'latest'
 
 runs:
-  using: docker
-  image: "${{ inputs.docker-image }}:${{ inputs.docker-image-tag }}"
-  args:
-    - ${{ inputs.app-path }}
+  using: "composite"
+  steps:
+    - name: Run
+      shell: bash
+      run: |
+        docker run --rm \
+           --volume ${PWD}:/workspace \
+           --workdir /workspace \
+           ${{ inputs.docker-image }}:${{ inputs.docker-image-tag }} \
+           ${{ inputs.app-path }}