Update jpegoptim URLs

When trying to update jpegoptim, Homebrew threw some errors:

```bash
$ brew upgrade jpegoptim
==> Upgrading 1 outdated package, with result:
jpegoptim 1.3.0
==> Upgrading jpegoptim
==> Downloading http://www.kokkonen.net/tjko/src/jpegoptim-1.3.0.tar.gz

curl: (7) Failed connect to www.kokkonen.net:80; Connection refused
Error: Failed to download resource "jpegoptim"
Download failed: http://www.kokkonen.net/tjko/src/jpegoptim-1.3.0.tar.gz
```

Checking the site, it appeared down. This apparently has happened before (#9642). The repo, however, still works and appears to have [recent activity](https://github.com/tjko/jpegoptim/commits/master).

This pull request changes the homepage to the repo URL and updates the URL to download from Github.