+ Bootstrap 3 URL, no longer called 'Twitter'

I've noticed one of the main devs nolonger works for Twitter (now works for GitHub), & "Twitter Bootstrap" is not on their website anymore, nor is "Built at Twitter by @mdo and @fat" like it was at v2.3.

Sorry, not trying to nit-pick; just following their lead ;)
Merge pull request #1 from tomByrer/patch-1

+ Bootstrap 3 URL, no longer called 'Twitter'