Make GitHub Actions cache Maven packages

Author: sideshowbarker

.github/workflows/build.yml

@@ -18,5 +18,11 @@ jobs:
         uses: actions/setup-java@v1
         with:
           java-version: ${{ matrix.java }}
+      - name: Cache Maven packages
+        uses: actions/cache@v2
+        with:
+          path: ~/.m2
+          key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+          restore-keys: ${{ runner.os }}-m2
       - name: Build with Maven
         run: mvn -Dfailonerror=false -B package