Remove deprecated gradle usage (#946)

Co-authored-by: kallestenflo <[email protected]>

Author: hezhangjian

build.gradle

@@ -64,8 +64,10 @@ subprojects {
     apply plugin: 'signing'
     apply plugin: 'biz.aQute.bnd.builder'
 
-    sourceCompatibility = JavaVersion.VERSION_1_8
-    targetCompatibility = JavaVersion.VERSION_1_8
+    java {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
 
     repositories {
         mavenCentral()