Fix another Stage 0 location (#212)

Author: benjie

spec/GraphQLOverHTTP.md

@@ -1,6 +1,6 @@
 ## GraphQL Over HTTP
 
-Note: **Stage 0: Preliminary** This spec is under active development, and not
+Note: **Stage 1: Proposal** This spec is under active development, and not
 ready for implementations yet. For more information, please see the
 [Roadmap](https://github.com/graphql/graphql-over-http/blob/master/ROADMAP.md)
 or