fixing typo.

Author: craiggwilson

src/MongoDB.Driver/IMongoIndexManager.cs

@@ -52,7 +52,7 @@ public interface IMongoIndexManager<TDocument>
         /// <param name="options">The options.</param>
         /// <param name="cancellationToken">The cancellation token.</param>
         /// <returns>
-        /// A task whos result is the name of the index that was created.
+        /// A task whose result is the name of the index that was created.
         /// </returns>
         Task<string> CreateOneAsync(IndexKeysDefinition<TDocument> keys, CreateIndexOptions options = null, CancellationToken cancellationToken = default(CancellationToken));