HB points out to heroku.com/deploy instead

dashboard-next.heroku.com is in beta right now, and it'll be a replacement of the existing dashboard.heroku.com. When that happens, you'll might need to update that url.

Updating it to www.heroku.com/deploy, it'll redirect to the proper place anytime, so no update will be needed!

And thanks for using it!!!

:metal:
Merge pull request #65 from raulb/patch-1

Update url for Heroku Button