fix readme to use library from github, close #13

Author: artemeff

README.md

@@ -9,7 +9,7 @@ Redis client for Elixir
 Add this to the dependencies:
 
 ```elixir
-{:exredis, "~> 0.1.0"}
+{ :exredis, github: "artemeff/exredis" }
 ```
 
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