Update ROADMAP.md

Author: jamesplease

ROADMAP.md

@@ -2,6 +2,13 @@
 
 This roadmap outlines future changes to React Request.
 
+### Next release
+
+* [ ] `doFetch` will return a Promise
+* [ ] A serial requests story will be more defined. Right now, it isn't super clear how to do it.
+
+### Sometime later
+
 * [ ] The caching implementation will be moved to `fetch-dedupe`. This is a non-breaking change.
 * [ ] Caching and deduplication will support an array, allowing for a more sophisticated system that
       supports multi-operational HTTP requests (GraphQL, for instance)