fix typo in README.md

Author: eagletmt

README.md

@@ -68,7 +68,7 @@ let g:ghcmod_hlint_options = ['--ignore=Redundant $']
 ![lint](http://cache.gyazo.com/3b64724ce2587e03761fe618457f1c2e.png)
 
 
-### :GhcModCheckAsnyc, :GhcModLintAsync, :GhcModCheckAndLintAsync
+### :GhcModCheckAsync, :GhcModLintAsync, :GhcModCheckAndLintAsync
 You can run check and/or lint asynchronously.
 
 This would be useful when you'd like to run check and/or lint automatically (especially on `BufWritePost`).