Add asset too large error code

Author: Steven-Chan

skygear/src/main/java/io/skygear/skygear/Error.java

@@ -208,6 +208,10 @@ public static enum Code {
          * Verification required error.
          */
         VERIFICATION_REQUIRED(128),
+        /**
+         * Asset size too large error.
+         */
+        ASSET_SIZE_TOO_LARGE(129),
         /**
          * Unexpected error.
          */