Fix `make book` on Mac

The BSD version of sed included on Mac OSX has very primitive argument parsing. When running `make book`, `fix-edit-button.sh`'s sed call fails because the `-i` flag tries to associate with the sed script. My fix checks if `--version` succeeds to decide if it should use the BSD or GNU syntax.
Apparently, we need to quote the `${sed_script}` -> `"${sed_script}"` or it won't work. (at least on the GNU version)