Update justified-nav.css

Removed unnecessary ms-linear-gradient prefix. There was never a stable release of IE that supported -ms- prefixed gradients, those were only in preview versions (stable IE10 supports both prefixed and unprefixed gradients). (source: http://lea.verou.me/2013/04/can-we-get-rid-of-gradient-prefixes/)
Merge pull request #9973 from coliff/patch-6

Update justified-nav.css (Removed unnecessary ms-linear-gradient prefix)
change `else if` to `else`
Merge pull request #9987 from wangsai/fix-typo

change `else if` to `else`
Fixes #9974

Added th selector in .table-row-variant mixin
Merge pull request #9999 from sqrt4/fix-9974

Fixes #9974
remove .btn-group

Removing this class--it's not used in the example and using it causes "bad things to happen." 

http://jsfiddle.net/josephtate/Jn6H4/
Merge pull request #10006 from jodytate/master

remove .btn-group
Update Grunt instruction links and wording
add David (david-dm.org) badge to monitor currentness of dependencies
Merge pull request #10011 from nschonni/patch-1

Update Grunt instruction links and wording
Use NPM version of grunt-html-validation

The package is now published, so the direct git url is no longer
required
Merge pull request #10034 from nschonni/use-published-version-for-grunt-html-validation

Use NPM version of grunt-html-validation
add cross-reference to .navbar-left/right in .pull-left/right docs
fix #10029
update outdated JSFiddle example
Merge pull request #10040 from twbs/pull-navbar-docs

add cross-reference to .navbar-left/right in .pull-left/right docs
Merge pull request #10012 from twbs/david-badge

add David (david-dm.org) badge to monitor currentness of dependencies
Merge branch 'master' of https://github.com/twbs/bootstrap into develop