Readme: update tmux version support to include 1.9a

Author: tony

README.rst

@@ -52,7 +52,7 @@ Project details
 ---------------
 
 ==============  ==========================================================
-tmux support    1.8, 1.9-dev
+tmux support    1.8, 1.9a, dev
 python support  2.6, 2.7, >= 3.3
 config support  yaml, json, python dict
 Source          https://github.com/tony/tmuxp