cmLocalGenerator: Fix trivial spelling error in code comment

Source/cmLocalGenerator.cxx

@@ -68,7 +68,7 @@
 #endif
 
 // List of variables that are replaced when
-// rules are expanced.  These variables are
+// rules are expanded.  These variables are
 // replaced in the form <var> with GetSafeDefinition(var).
 // ${LANG} is replaced in the variable first with all enabled
 // languages.