fix mina rake bug

[devvmh]

This change fixes a bug that prevents me from using mina rake:

uniqueway-devin:uniqueway devin$ mina rake[oneoff:test_task]
mina aborted!
NoMethodError: undefined method `deploy_to!' for main:Object
Did you mean?  deploy
/Users/devin/.rvm/gems/ruby-2.3.0/gems/mina-1.0.0.beta5/tasks/mina/rails.rb:97:in `block (2 levels) in <top (required)>'
/Users/devin/.rvm/gems/ruby-2.3.0/gems/mina-1.0.0.beta5/lib/mina/application.rb:16:in `run'
/Users/devin/.rvm/gems/ruby-2.3.0/gems/mina-1.0.0.beta5/bin/mina:4:in `<top (required)>'
/Users/devin/.rvm/gems/ruby-2.3.0/bin/mina:23:in `load'
/Users/devin/.rvm/gems/ruby-2.3.0/bin/mina:23:in `<main>'