Clarify filedropper error message

lib/msf/core/exploit/file_dropper.rb

@@ -122,7 +122,7 @@ module Exploit::FileDropper
     end
 
     @dropped_files.each do |f|
-      print_warning("This exploit may require manual cleanup of: #{f}")
+      print_warning("This exploit may require manual cleanup on the target of: #{f}")
     end
 
   end