Typo fixed in cluster.markdown

Author: YevKov

cluster.markdown

@@ -163,7 +163,7 @@ session.save_path = "seed[]=host1:port1&seed[]=host2:port2&seed[]=hostN:portN&ti
 Set this variable to "rediscluster" to inform phpredis that this is a cluster instance.
 
 ### session.save_path
-The save path for cluster based session storage takes the form of a PHP GET request, and requires that you specify at least on `seed` node.  Other options you can specify are as follows:
+The save path for cluster based session storage takes the form of a PHP GET request, and requires that you specify at least one `seed` node.  Other options you can specify are as follows:
 
 * _timeout (double)_:  The amount of time phpredis will wait when connecting or writing to the cluster.
 * _read_timeout (double)_: The amount of time phpredis will wait for a result from the cluster.