DOCS-15649 fix limiations wording (#92)

Author: Dave Cuthbert

source/reference/limitations.txt

@@ -89,7 +89,7 @@ Sharded Clusters
 - The shard key cannot be :ref:`refined <shard-key-refine>` while
   synchronizing.
 - The shard key cannot be modified using :dbcommand:`reshardCollection`
-  during resharding.
+  during syncing.
 - The maximum number of :ref:`shard key indexes
   <sharding-shard-key-indexes>` is one lower than normal, 63 instead of
   64.