Fix typo version

https://github.com/yiisoft/yii2/blob/master/extensions/redis/Cache.php#L16

docs/guide/caching.md

@@ -62,7 +62,7 @@ is a summary of the available cache components:
   balancers, etc.)
 
 * [[\yii\caching\RedisCache]]: implements a cache component based on [Redis](http://redis.io/) key-value store
-  (redis version 2.6 or higher is required).
+  (redis version 2.6.12 or higher is required).
 
 * [[\yii\caching\WinCache]]: uses PHP [WinCache](http://iis.net/downloads/microsoft/wincache-extension)
   ([see also](http://php.net/manual/en/book.wincache.php)) extension.