Update 19-automattic.md

- "evidenced already the considerable volunteer time", not sure if this is missing a 'by' as in "evidenced already by the considerable volunteer time", so didn't include it.
For reference, about the corrections of big sites' names:
- Gigaom: https://about.gigaom.com/
- TechCrunch: http://techcrunch.com/about/
- Scobleizer: http://scobleizer.com/ (ironically, the last post on his blog is about moving on to fb/twitter/G+)