Merge pull request #13461 from patrickhlauke/docs-dropdown-sr-only

Remove sr-only from components/dropdowns example
bump grunt-css-flip to ~0.2.2
Merge pull request #13433 from watilde/fixed-navbar-radius-of-example-at-docs

Fixed navbar radius of example at docs
Improve accessibility of close buttons in modals & alerts

Adds textual caption to the close buttons. The "X" multiplication sign isn't very meaningful to screenreaders.

Credit: https://github.com/paypal/bootstrap-accessibility-plugin
Per:
    https://github.com/paypal/bootstrap-accessibility-plugin/blob/master/README.md#alert
    https://github.com/paypal/bootstrap-accessibility-plugin/blob/master/README.md#modal-dialog
document #13390
mark Android Firefox as officially supported
Wall of browser bugs: formatting tweaks
Merge pull request #13495 from twbs/android-firefox

Officially support Android Firefox
Merge pull request #13493 from twbs/close-btn-access

Improve accessibility of close buttons in modals & alerts
include RTL CSS CDN URL in Download docs
add RTL CSS files to "What's included" section of docs
emphasize that bootstrap-rtl.css & bootstrap.css should not be used together
replace js scrollspy test for default behavior
Fix .visible-print deprecation version #.
import rules from Ratchet's JSCS config with which we already comply
Merge pull request #13506 from twbs/jscs-ratchet

import rules from Ratchet's JSCS config with which we already comply
Allow for resetText of a button to be a falsey value; fixes #13466
temporarily lock grunt-jscs-checker to v0.4.0

Per #13512 & https://github.com/mdevils/node-jscs/issues/357
update-shrinkwrap
bump grunt-jscs-checker to v0.4.1; refs #13512