-fix typo in docs of deprecated MacroAddFileDependencies.cmake

Patch on the mailing list by Serge Ziryukin.

Alex

Modules/MacroAddFileDependencies.cmake

@@ -1,6 +1,6 @@
 # - MACRO_ADD_FILE_DEPENDENCIES(<_file> depend_files...)
 # Using the macro MACRO_ADD_FILE_DEPENDENCIES() is discouraged. There are usually
-# better ways to specifiy the correct dependencies.
+# better ways to specify the correct dependencies.
 #
 # MACRO_ADD_FILE_DEPENDENCIES(<_file> depend_files...) is just a convenience 
 # wrapper around the OBJECT_DEPENDS source file property. You can just