Specifying `travis_event` in settings causes failure

While following the instructions for setting up the bot, if you have something like the following in your settings yml:

travis_event:
  enabled_repos:
    - notchrisarcand/sandbox

You will receive the following fatal error trying to start the bot:

14:26:23 travis_listener.1 | rake aborted!
14:26:23 travis_listener.1 | Travis::Client::NotFound: {"file":"not found"}
14:26:23 travis_listener.1 | /Users/carcand/workspace/manageiq/miq_bot/lib/travis_event/listener.rb:36:in `block in travis_repos'
14:26:23 travis_listener.1 | /Users/carcand/workspace/manageiq/miq_bot/lib/travis_event/listener.rb:36:in `collect'
14:26:23 travis_listener.1 | /Users/carcand/workspace/manageiq/miq_bot/lib/travis_event/listener.rb:36:in `travis_repos'
14:26:23 travis_listener.1 | /Users/carcand/workspace/manageiq/miq_bot/lib/travis_event/listener.rb:22:in `monitor'
14:26:23 travis_listener.1 | /Users/carcand/workspace/manageiq/miq_bot/lib/travis_event/listener.rb:17:in `run'
14:26:23 travis_listener.1 | /Users/carcand/workspace/manageiq/miq_bot/lib/tasks/travis_event_listener.rake:4:in `block (2 levels) in <top (required)>'
14:26:23 travis_listener.1 | /Users/carcand/.rbenv/versions/2.2.5/bin/bundle:23:in `load'
14:26:23 travis_listener.1 | /Users/carcand/.rbenv/versions/2.2.5/bin/bundle:23:in `<main>'
14:26:23 travis_listener.1 | Tasks: TOP => travis_event_listener:run
14:26:23 travis_listener.1 | (See full trace by running task with --trace)
14:26:23 travis_listener.1 | exited with code 1
14:26:23 system            | sending SIGTERM to all processes

Whatever causes it might want to be handled more gracefully.

Start in lib/travis_event/listener.rb at line 36, where travis_repos is shown failing, and inspect the listener task in lib/tasks/travis_event_listener.rake. Reproduce the startup with the provided travis_event settings and determine how the Travis::Client::NotFound failure should be handled gracefully; done means the bot no longer aborts fatally for this configuration.