FindGTest: Fix documented GTEST_MSVC_SEARCH default value

Documentation updates in commit v3.5.0-rc1~124^2~2 (FindGTest: Add
imported targets and update documentation, 2015-12-10) accidentally
changed the documented default to the wrong value.  Restore the
documentation to refer to the actual default used in the implementation.

Modules/FindGTest.cmake

@@ -49,8 +49,8 @@
 #   The root directory of the Google Test installation (may also be
 #   set as an environment variable)
 # ``GTEST_MSVC_SEARCH``
-#   If compiling with MSVC, this variable can be set to ``MD`` or
-#   ``MT`` (the default) to enable searching a GTest build tree
+#   If compiling with MSVC, this variable can be set to ``MT`` or
+#   ``MD`` (the default) to enable searching a GTest build tree
 #
 #
 # Example usage