Bump actions/cache from 2 to 2.1.5 (apache#64)

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>

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

Author: dependabot[bot]

.github/workflows/maven.yml

@@ -32,7 +32,7 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2.3.4
-    - uses: actions/cache@v2
+    - uses: actions/cache@v2.1.5
       with:
         path: ~/.m2/repository
         key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}