Bump actions/cache from v2.1.4 to v2.1.5

Bumps [actions/cache](https://github.com/actions/cache) from v2.1.4 to v2.1.5.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2.1.4...1a9e213)

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/ci.yml

@@ -46,7 +46,7 @@ jobs:
         run: echo "::set-output name=directory::$(composer config cache-dir)"
 
       - name: Cache composer dependencies
-        uses: actions/[email protected].4
+        uses: actions/[email protected].5
         with:
           path: ${{ steps.composer-cache.outputs.directory }}
           key: ${{ matrix.php }}-composer-${{ hashFiles('**/composer.lock') }}