Update readme [ci skip]
Forcing travis ci to use bundler 1.5.1.

https://github.com/travis-ci/travis-ci/issues/1806
https://github.com/bundler/bundler/issues/2780
Changing the way of alchemy menubar rendering.

From now we let rails render a partial for the menubar, removed the helper ´alchemy_menu_bar´ and do not build the bar with javascript anymore.

Old usage:  <%= alchemy_menu_bar %>
New usage: <%= render "alchemy/menubar/show" %>