Update source/core/sharding.txt

typo

Author: monkey101

source/core/sharding.txt

@@ -336,7 +336,7 @@ server data is only read in the following situations:
 
 If all three config servers are inaccessible, you can continue to use
 the cluster as long as you don't restart the :program:`mongos`
-instances until the after config servers are accessible again. If you
+instances until after config servers are accessible again. If you
 restart the :program:`mongos` instances and there are no accessible
 config servers, the :program:`mongos` would be unable to direct
 queries or write operations to the cluster.