Use new GitHub Actions to build PRs

.github/workflows/pullrequest.yml

@@ -0,0 +1,29 @@
+name: Build Pull Request
+
+on: [pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions/cache@v1
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-
+      - name: Set up JDK 1.8
+        uses: actions/setup-java@v1
+        with:
+          java-version: 1.8
+      - name: Build with Maven
+        run: mvn -B package
+      - name: Archive artifacts
+        uses: actions/upload-artifact@v1
+        if: success()
+        with:
+          name: Geyser
+          path: target/Geyser.jar