Update actions/cache uses to v2

examples/slim-framework.yml

@@ -21,7 +21,7 @@ jobs:
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"
       - name: Cache composer dependencies
-        uses: actions/cache@v1
+        uses: actions/cache@v2
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           # Use composer.json for key, if composer.lock is not committed.