switch to container-based docker builds

travis-ci now is testing docker container-based builds, which have a lot
of advantages and could speed things up significantly:

    http://blog.travis-ci.com/2014-12-17-faster-builds-with-container-based-infrastructure/

this mean no sudo, so we cant use apt-get to install mplayer and ffmpeg.
just commenting them out for now which should cause a failure, but that
will be the starting point to working around them.

also enabling bundler cache, which is available for free projects with
this build system, and should speed up installs greatly.

.travis.yml

@@ -1,4 +1,6 @@
+sudo: false
 language: ruby
+cache: bundler
 rvm:
  - 1.8.7
  - 1.9.2
@@ -9,8 +11,8 @@ rvm:
  - ruby-head
 
 before_install:
- - sudo apt-get update -qq
- - sudo apt-get install -qq -y mplayer ffmpeg
+ # - sudo apt-get update -qq
+ # - sudo apt-get install -qq -y mplayer ffmpeg
 
 matrix:
   allow_failures: