don't build on Java 8

.github/workflows/gradle.yml

@@ -6,18 +6,6 @@ name: Java CI with Gradle
 on: [push, pull_request]
 
 jobs:
-  build-8:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v2
-    - name: Set up JDK 1.8
-      uses: actions/setup-java@v1
-      with:
-        java-version: 1.8
-    - name: Grant execute permission for gradlew
-      run: chmod +x gradlew
-    - name: Build with Gradle
-      run: ./gradlew build
   build-11:
     runs-on: ubuntu-latest
     steps: