Update to use actions-plan-preview image 1.7.2 (#10)

* Update image tag version

* Fix actions-plan-preview version

* Fix README

Dockerfile

@@ -1 +1 @@
-FROM gcr.io/pipecd/actions-plan-preview:1.6.0
+FROM gcr.io/pipecd/actions-plan-preview:1.7.2

README.md

@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-latest
     if: "github.event_name == 'pull_request'"
     steps:
-      - uses: pipe-cd/actions-plan-preview@v1.6.0
+      - uses: pipe-cd/actions-plan-preview@v1.7.2
         with:
           address: ${{ secrets.PIPECD_API_ADDRESS }}
           api-key: ${{ secrets.PIPECD_PLAN_PREVIEW_API_KEY }}
@@ -50,7 +50,7 @@ jobs:
     runs-on: ubuntu-latest
     if: "github.event_name == 'issue_comment' && github.event.issue.pull_request && startsWith(github.event.comment.body, '/pipecd plan-preview')"
     steps:
-      - uses: pipe-cd/actions-plan-preview@v1.6.0
+      - uses: pipe-cd/actions-plan-preview@v1.7.2
         with:
           address: ${{ secrets.PIPECD_API_ADDRESS }}
           api-key: ${{ secrets.PIPECD_PLAN_PREVIEW_API_KEY }}