correct java version

build.gradle

@@ -41,7 +41,11 @@ allprojects {
 project(":desktop") {
     apply plugin: "java-library"
 
-
+	java {
+		sourceCompatibility = JavaVersion.VERSION_1_8
+		targetCompatibility = JavaVersion.VERSION_1_8
+	}
+	
     dependencies {
         implementation project(":core")
         api "com.badlogicgames.gdx:gdx-backend-lwjgl:$gdxVersion"
@@ -65,7 +69,11 @@ project(":desktop") {
 
 project(":core") {
     apply plugin: "java-library"
-
+	
+	java {
+		sourceCompatibility = JavaVersion.VERSION_1_8
+		targetCompatibility = JavaVersion.VERSION_1_8
+	}
 
     dependencies {
         api "com.badlogicgames.gdx:gdx:$gdxVersion"