first attempt to have CI on master and PRs

.github/workflows/gradle-build-pr.yml

@@ -0,0 +1,18 @@
+name: Run Gradle on PRs
+
+on: [push,pull_request]
+
+jobs:
+  gradle:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v1
+    - uses: actions/setup-java@v1
+      with:
+        java-version: 11
+    - uses: eskatos/gradle-command-action@v1
+      with:
+        arguments: build