Run command adding colon on bamboo and aspen stacks

[gbenedict]

With 4.0.1 and rake 9.0.2.2 against the bamboo-ree-1.8.7 stack, I'm getting the following error when deploying:

!    `run:rake db:migrate` is not a heroku command.

There shouldn't be a colon between run and rake. I believe with the latest Heroku API update, this is no longer needed and actually breaks the deploy.

You can see this in the run command on line 50 of https://github.com/fastestforward/heroku_san/blob/master/lib/heroku_san/stage.rb