Remove broken link to logo author's website
Remove broken link to logo author's website

The website doesn't exist anymore and no comparable online presence
exists.

Fixes https://github.com/prometheus/docs/issues/794

Signed-off-by: Julius Volz <d7748b1e6f41fd74500c5ccae0980eab88c2ef61@gmail.com>

prometheus/docs,ddfreyne/prometheus-docs,ddfreyne/prometheus-docs,ddfreyne/prometheus-docs,prometheus/docs,ddfreyne/prometheus-docs,prometheus/docs