fixed grammar error

Author: brian-swart

docs/vs-2015/test/isolating-code-under-test-with-microsoft-fakes.md

@@ -140,7 +140,7 @@ Microsoft Fakes help you isolate the code you are testing by replacing other par
 
     ```  
 
-     The special piece of magic here is the class `StubIStockFeed`. For every interface in the referenced assembly, the Microsoft Fakes mechanism generates a stub class. The name of the stub class is the derived from the name of the interface, with "`Fakes.Stub`" as a prefix, and the parameter type names appended.  
+     The special piece of magic here is the class `StubIStockFeed`. For every interface in the referenced assembly, the Microsoft Fakes mechanism generates a stub class. The name of the stub class is derived from the name of the interface, with "`Fakes.Stub`" as a prefix, and the parameter type names appended.  
 
      Stubs are also generated for the getters and setters of properties, for events, and for generic methods. For more information, see [Using stubs to isolate parts of your application from each other for unit testing](../test/using-stubs-to-isolate-parts-of-your-application-from-each-other-for-unit-testing.md).