Bump actions/cache from 2 to 2.1.5

Bumps [actions/cache](https://github.com/actions/cache) from 2 to 2.1.5.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2...v2.1.5)

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

.github/workflows/maven.yml

@@ -35,7 +35,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Set up cache for ~./m2/repository
-        uses: actions/cache@v2
+        uses: actions/cache@v2.1.5
         with:
           path: ~/.m2/repository
           key: maven-${{ matrix.os }}-java${{ matrix.java }}-${{ hashFiles('**/pom.xml') }}