update gradle version (#191)

Author: realDuYuanChao

.github/workflows/gradle.yml

@@ -12,10 +12,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up JDK 14
+    - name: Set up JDK 12
       uses: actions/setup-java@v1
       with:
-        java-version: 14
+        java-version: 12
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew
     - name: Build with Gradle