Update source/release-notes/2.2.txt

Fix accidental indentation.

Author: matulef

source/release-notes/2.2.txt

@@ -96,7 +96,7 @@ We recommend the following upgrade procedure for a sharded cluster:
   procedure for replica sets <2.2-upgrade-replica-set>` for each of
   the shards.
 
- - re-enable the balancer.
+- re-enable the balancer.
 
 If your cluster uses authentication, you must upgrade the components in 
 the order above.  If your cluster does not use authentication, you can