fix format issue (#1031)

Author: MongoCaleb

source/sdk/dotnet/data-types/field-types.txt

@@ -60,7 +60,7 @@ MongoDB.Bson Types
 
 Guid and ObjectId Properties
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-``Guid`` is .. versionadded:: 10.2.0-beta.1
+.. versionadded:: 10.2.0-beta.1
 
 ``MongoDB.Bson.ObjectId`` is a MongoDB-specific 12-byte unique value, while the 
 built-in .NET type ``Guid`` is a 16-byte universally-unique value. Both types are