Fix gitignore.io plugin URL

gitignore.io now requires calls to be made to www.gitignore.io (instead of just gitignore.io)

See January 6, 2014 update on http://www.gitignore.io/cli

I also switched to using ping's timeout parameter instead of the timeout util for OSX compatibility. And I silenced curl's output, since it would otherwise print out the progress of downloading the gitignore.io list on every launch of fish.