Single MongoClient Credential (#249)

Author: mongoKart

source/upgrade/v3.txt

@@ -135,4 +135,7 @@ Version 3.0 Breaking Changes
      };
 
      // Serialize the document to JSON using the configured settings
-     var json = document.ToJson(jsonWriterSettings);
+     var json = document.ToJson(jsonWriterSettings);
+
+- The ``MongoClient`` constructor accepts only one ``Credential`` object instead of an
+  array.