.travis.yml: Use Ruby 2.0.0 on Linuxbrew
.travis.yml: Use Ruby 2.0.0 on Linuxbrew

Fix the errror:
Installing simplecov-html 0.10.0
NoMethodError: undefined method `spec' for nil:NilClass
An error occurred while installing simplecov (0.11.2)

Closes Linuxbrew/linuxbrew#798

Linuxbrew/brew,rwhogg/brew,Linuxbrew/brew,rwhogg/brew,hanxue/linuxbrew,maxim-belkin/brew,rwhogg/brew,maxim-belkin/brew,hanxue/linuxbrew,Linuxbrew/brew,Linuxbrew/brew,maxim-belkin/brew,hanxue/linuxbrew