Bump actions/cache from 2.1.5 to 2.1.6

Bumps [actions/cache](https://github.com/actions/cache) from 2.1.5 to 2.1.6.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2.1.5...v2.1.6)

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

Author: dependabot[bot]

.github/workflows/maven.yml

@@ -36,7 +36,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Set up cache for ~./m2/repository
-        uses: actions/[email protected].5
+        uses: actions/[email protected].6
         with:
           path: ~/.m2/repository
           key: maven-${{ matrix.os }}-java${{ matrix.java }}-${{ hashFiles('**/pom.xml') }}