Bump actions/cache from v1 to v2 (#10)

Bumps [actions/cache](https://github.com/actions/cache) from v1 to v2.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v1...b820478)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/continuous-integration.yml

@@ -33,7 +33,7 @@ jobs:
               run: echo "::set-output name=dir::$(composer config cache-files-dir)"
 
             - name: Cache dependencies
-              uses: actions/cache@v1
+              uses: actions/cache@v2
               with:
                   path: ${{ steps.composer-cache.outputs.dir }}
                   key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}