Clarify mention of Unicode in Features.md (facebook#30)

Summary:
I've seen someone interpret this document as saying that Hermes excludes support for Unicode in general. This is my attempt to make that interpretation less likely.
Pull Request resolved: facebook#30

Reviewed By: motiz88

Differential Revision: D16244822

Pulled By: avp

fbshipit-source-id: 1298846d06ed18d2af02fbf9945b88c54840c447

doc/Features.md

@@ -31,7 +31,7 @@ Hermes plans to target ECMAScript 2015 (ES6), with some carefully considered exc
 - Realms
 - `with` statements
 - Local mode `eval()` (use and introduce local variables)
-- Unicode and sticky flags in `RegExp`
+- `/u` (Unicode) and `/y` (sticky) flags in `RegExp`
 - `Intl` API
 - `Symbol.species` and its interactions with JS library functions
 - `Symbol.unscopables` (Hermes does not support `with`)