Remove global gitignore lines

[Luukyb]

A good practice for extension files that should never, ever, being added to git (.DS_Store, .vagrant, sass-cache ...) should be ignored using global gitignore file on your computer, not specially on the gitignore file of the project.
On how to do it, see "Create a global .gitignore" https://help.github.com/articles/ignoring-files/

I suggest removing the following lines from the gitignore file :
.vagrant/
.DS_Store
.bundle
.ruby-version
.sass-cache

[leolandotan]

I think the also the .idea maybe?

[generalredneck]

@Luukyb Feel free to put in a PR. I'm all for it.