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/ci.yml

@@ -24,7 +24,7 @@ jobs:
       - name: 'Check out repository'
         uses: actions/[email protected]
       - name: 'Cache local Maven repository'
-        uses: actions/[email protected].5
+        uses: actions/[email protected].6
         with:
           path: ~/.m2/repository
           key: maven-${{ hashFiles('**/pom.xml') }}
@@ -51,7 +51,7 @@ jobs:
       - name: 'Check out repository'
         uses: actions/[email protected]
       - name: 'Cache local Maven repository'
-        uses: actions/[email protected].5
+        uses: actions/[email protected].6
         with:
           path: ~/.m2/repository
           key: maven-${{ hashFiles('**/pom.xml') }}
@@ -80,7 +80,7 @@ jobs:
       - name: 'Check out repository'
         uses: actions/[email protected]
       - name: 'Cache local Maven repository'
-        uses: actions/[email protected].5
+        uses: actions/[email protected].6
         with:
           path: ~/.m2/repository
           key: maven-${{ hashFiles('**/pom.xml') }}