Update README.md

spelling fix

Author: glensc

README.md

@@ -6,7 +6,7 @@ reconfigures itself when a linked cluster member redeploys, joins or leaves.
 
 ## Version
 
-The availabe version can be found here: https://hub.docker.com/r/dockercloud/haproxy/tags/
+The available version can be found here: https://hub.docker.com/r/dockercloud/haproxy/tags/
  - `latest` is buit againt master brach
  - `staging` is built againt staging branch
  - `x.x.x` is built againt git tags on github