Configure caching for github actions

.github/workflows/gradle.yml

@@ -9,6 +9,12 @@ jobs:
 
     steps:
     - uses: actions/checkout@v1
+    - uses: actions/cache@v1
+      with:
+        path: ~/.gradle/caches
+        key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle') }}
+        restore-keys: |
+          ${{ runner.os }}-gradle-
     - name: Set up JDK 11
       uses: actions/setup-java@v1
       with: