[chore] Update showcase image in CI (#94)

Author: noahdietz

packages/gapic-generator/.circleci/config.yml

@@ -93,7 +93,7 @@ jobs:
   showcase:
     docker:
       - image: python:3.7-slim
-      - image: gcr.io/gapic-showcase/gapic-showcase:0.0.12
+      - image: gcr.io/gapic-images/gapic-showcase:0.0.12
     steps:
       - checkout
       - run: