Fix arguments of sed command for Mac OS.

On MacOS `sed -i -e xxxx` creates a backup file whose name is `xxxx-e`.
This change prevents from creating such a backup file.
Here is a related article on Stackoverflow.
http://stackoverflow.com/questions/5171901/sed-command-find-and-replace-in-file-and-overwrite-file-doesnt-work-it-empties#comment40178991_5171935

I tested my code on only Mac OS.