Add @publicapi

Author: martinbonnin

src/main/java/graphql/Enums.java

@@ -7,6 +7,7 @@
 /**
  * The enums that are understood by graphql-java
  */
+@PublicApi
 public class Enums {
     public static final String ON_ERROR = "OnError";
     public static final String ON_ERROR_PROPAGATE = "PROPAGATE";