Merge pull request #7 from hhu-propra2/tom_branch

change CI

.github/workflows/gradle.yml

@@ -1,7 +1,12 @@
 name: Java CI
 
-on: [push, pull_request]
-
+on: 
+  push:
+    branches: 
+      - master
+  pull_request:
+    branches: 
+      - master
 jobs:
   build:
 
@@ -9,10 +14,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up JDK 11
+    - name: Set up JDK 13
       uses: actions/setup-java@v1
       with:
-        java-version: 11
+        java-version: 13
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew
     - name: Build with Gradle