Fix #10948: Clarify navbar example target in docs

According to comment on https://github.com/twbs/bootstrap/issues/10948#issuecomment-25751889 .

Correct grammar

Jekyll is the third person singular (it), so it should be 'its documentation', not 'their documentation'.

Remove .ruby-version from excludes

Indent banner to match the *'s

add iOS and versions to Safari percent rounding warning; fixes #10723

document that multiple navbars aren't supported by default

Added abridged form of 'What's included' docs to README

Better documentation and optimized examples for grid classes

Apply help-block class to help text in customize.html

Remove "Remove margin on the body" from base css docs

table contextual classes docs: .col-lg-* => .col-xs-*

use .col-xs-* in "Forms: Column Sizing" docs so more responsive

Normalize did that.

Remove .ruby-version due to https://github.com/twbs/bootstrap/commit/4f20a29c329aa58919919426cbd2190fabfdb723

Update qunit dependency

Update Gruntfile.js fixing undefined jQuery check

The check to see if jQuery was defined as incorrect causing the "Bootstrap requires jQuery" message to only be displayed if jQuery is defined and has a value which equates to `false`.