use java 11 in github actions

Author: Alexander Furer

.github/workflows/gradle.yml

@@ -15,11 +15,12 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
-    - name: Set up JDK 1.8
-      uses: actions/setup-java@v1
+    - name: checkout project
+      uses: actions/checkout@v2
+    - name: Set up JDK
+      uses: actions/setup-java@v2
       with:
-        java-version: 1.8
+        java-version: 11
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew
     - name: Build with Gradle