Land rapid7#3413, improved FileDropper cleanup message

Author: wvu

lib/msf/core/exploit/file_dropper.rb

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