Mark model fields final

Summary: These are already considered immutable, but not marked in their class.

Reviewed By: emilsjolander

Differential Revision: D6759564

fbshipit-source-id: 810dc8a9730fb330760d2aedecafcea81cf25cb1

java/com/facebook/yoga/YogaLogLevel.java

@@ -20,7 +20,7 @@ public enum YogaLogLevel {
   VERBOSE(4),
   FATAL(5);
 
-  private int mIntValue;
+  private final int mIntValue;
 
   YogaLogLevel(int intValue) {
     mIntValue = intValue;