Add compileOptions for video_player >= 0.8.0

Those are added to new flutter projects as well

example/android/app/build.gradle

@@ -17,6 +17,11 @@ apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 android {
     compileSdkVersion 27
 
+    compileOptions {
+        sourceCompatibility 1.8
+        targetCompatibility 1.8
+    }
+
     lintOptions {
         disable 'InvalidPackage'
     }