CMakeLists: print warning about missing Mallets instrument instead of Stk

The Vibed plugin has nothing to do with STK. Instead the Mallets
instrument plugin is meant. Fixed.
(cherry picked from commit a0ef88908c)

CMakeLists.txt

@@ -179,7 +179,7 @@ IF(WANT_STK)
 	ELSE(STK_FOUND)
 		SET(STK_INCLUDE_DIR "")
 		SET(STATUS_STK "not found, please install libstk0-dev (or similiar) "
-			"if you require the Vibed Instrument")
+			"if you require the Mallets instrument")
 	ENDIF(STK_FOUND)
 ENDIF(WANT_STK)