Fix a typo in README

This is just a minor fix. Please see the diff.

README.md

@@ -31,7 +31,7 @@ From source:
 The official Redis documentation does a great job of explaining each command in
 detail (http://redis.io/commands). redis-py exposes two client classes that
 implement these commands. The StrictRedis class attempts to adhere to the
-official official command syntax. There are a few exceptions:
+official command syntax. There are a few exceptions:
 
 * SELECT: Not implemented. See the explanation in the Thread Safety section
   below.