Add github actions caching step

Signed-off-by: NTobias Schneider <Tobias.Schneider@Tobsch.org>

.github/workflows/maven.yml

@@ -13,5 +13,12 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: 1.8
+    - name: Cache local Maven repository
+      uses: actions/cache@v2
+      with:
+        path: ~/.m2/repository
+        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+        restore-keys: |
+          ${{ runner.os }}-maven-
     - name: Build with Maven
       run: mvn -B verify --file pom.xml