Change MakeUnique -> std::make_unique in docs

docs/gmock_cheat_sheet.md

@@ -140,7 +140,7 @@ To customize the default action for functions with return type `T`, use
   // Sets the default action for return type std::unique_ptr<Buzz> to
   // creating a new Buzz every time.
   DefaultValue<std::unique_ptr<Buzz>>::SetFactory(
-      [] { return MakeUnique<Buzz>(AccessLevel::kInternal); });
+      [] { return std::make_unique<Buzz>(AccessLevel::kInternal); });
 
   // When this fires, the default action of MakeBuzz() will run, which
   // will return a new Buzz object.