Build compatible bytecode with newer JDKs

Fix #2898, close #2899

build.gradle

@@ -40,6 +40,16 @@ subprojects {
         maven { url "https://jitpack.io" }
         maven { url "http://oss.sonatype.org/content/repositories/snapshots" }
     }
+
+    if (getPlugins().hasPlugin('java')) {
+        tasks.withType(JavaCompile) {
+            // If building with JDK 9+, we need additional flags to generate compatible bytecode
+            if (JavaVersion.current() > JavaVersion.VERSION_1_8) {
+                options.compilerArgs += ['--release', '8']
+            }
+        }
+    }
+
     afterEvaluate { module ->
         if (getPlugins().hasPlugin('com.android.library') ||
             getPlugins().hasPlugin('com.android.application')) {

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,6 @@
+#Sat Jun 20 05:36:13 PDT 2020
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.5-all.zip