Bump actions/cache from v1 to v2

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] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
         java: [8, 11]
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/cache@v1
+      - uses: actions/cache@v2
         with:
           path: ~/.m2/repository
           key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}