Update to use V3 of API

[schneems]

Platform-api gem

Use the platform-api gem which is a Heroku v3 API gem.

Heroku 16 Compliant

• Does not support Ruby 1.9.3

Replace Test Unit with Minitest

This isn't strictly necessary, but the test format of Test Unit became practically unreadable and was hurting my eyes.

Known Issues

• 304 etag based caching is disabled due to Calls to /apps use etag even though Endpoint does not support it platform-api#73

• deployed? could be improved to check for build success and then that the formations endpoint to ensure that web was up.

[jkutner]

I think we can remove the CLI by replacing the teardown task with something like this:

  task :teardown_travis do
    key_to_delete = `cat ~/.ssh/id_rsa.pub`
    keys_json = `curl -sn https://api.heroku.com/account/keys -H "Accept: application/vnd.heroku+json; version=3"`
    require 'json'
    keys = JSON.parse(keys_json)
    keys.each do |key|
      key_parts = key["public_key"].split(" ")
      if key_parts[1] == key_to_delete.split(" ")[1]
        puts "Deleting #{key_parts[1]}"
        `curl -sn -X DELETE https://api.heroku.com/account/keys/#{key["id"]} -H "Accept: application/vnd.heroku+json; version=3"`
      end
    end
  end