Update error codes

Author: lgebhardt

README.md

@@ -720,13 +720,14 @@ module JSONAPI
   KEY_NOT_INCLUDED_IN_URL = 110
   INVALID_INCLUDE = 112
   RELATION_EXISTS = 113
-  INVALID_SORT_PARAM = 114
+  INVALID_SORT_CRITERIA = 114
   INVALID_LINKS_OBJECT = 115
   TYPE_MISMATCH = 116
   INVALID_PAGE_OBJECT = 117
   INVALID_PAGE_VALUE = 118
   INVALID_FIELD_FORMAT = 119
   INVALID_FILTERS_SYNTAX = 120
+  SAVE_FAILED = 121
   FORBIDDEN = 403
   RECORD_NOT_FOUND = 404
   UNSUPPORTED_MEDIA_TYPE = 415