add maven cache

.github/workflows/maven.yml

@@ -13,5 +13,10 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: 1.8
+    - name: Cache Maven Repository
+        uses: actions/cache@v1
+        with:
+          path: ~/.m2
+          key: jetlinks-community-maven-repository
     - name: Build with Maven
-      run: mvn -B package
+      run: mvn -B package