Update mod_suexec.rb

On Yosemite (10.10), `brew doctor` throws an error because the mod_suexec formula only contains URLs for Mountain Lion and Mavericks. This commit provides a URL to the default Apache version (2.4.9) included with Yosemite.

(I don't use mod_suexec, and thought I read somewhere this formula is broken, but at least this fixes the error on Yosemite.)

```bash
> ~/Desktop/ brew doctor
Error: Failed to import: mod_suexec
formulae require at least a URL
```