Merge branch 'master' into v4

Conflicts:
	.gitignore
	Gruntfile.js
	_config.yml
	dist/css/bootstrap-theme.css
	dist/css/bootstrap-theme.min.css
	dist/css/bootstrap.css
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css
	dist/js/bootstrap.js
	dist/js/bootstrap.min.js
	docs/_includes/components/navbar.html
	docs/_includes/components/progress-bars.html
	docs/_includes/css/grid.html
	docs/_includes/css/overview.html
	docs/_includes/customizer-variables.html
	docs/_includes/getting-started/accessibility.html
	docs/_includes/getting-started/browser-device-support.html
	docs/_includes/getting-started/community.html
	docs/_includes/getting-started/disabling-responsiveness.html
	docs/_includes/getting-started/download.html
	docs/_includes/getting-started/examples.html
	docs/_includes/getting-started/license.html
	docs/_includes/getting-started/third-party-support.html
	docs/_includes/js/alerts.html
	docs/_includes/js/buttons.html
	docs/_includes/js/carousel.html
	docs/_includes/js/collapse.html
	docs/_includes/js/dropdowns.html
	docs/_includes/js/modal.html
	docs/_includes/js/popovers.html
	docs/_includes/js/scrollspy.html
	docs/_includes/js/tabs.html
	docs/_includes/js/tooltips.html
	docs/_includes/js/transitions.html
	docs/_includes/nav/javascript.html
	docs/_includes/nav/main.html
	docs/about.html
	docs/assets/css/docs.min.css
	docs/assets/css/src/docs.css
	docs/assets/js/customize.min.js
	docs/assets/js/raw-files.min.js
	docs/assets/js/src/customizer.js
	docs/dist/css/bootstrap-theme.css
	docs/dist/css/bootstrap-theme.min.css
	docs/dist/css/bootstrap.css
	docs/dist/css/bootstrap.css.map
	docs/dist/css/bootstrap.min.css
	docs/dist/js/bootstrap.js
	docs/dist/js/bootstrap.min.js
	docs/migration.html
	js/affix.js
	js/alert.js
	js/button.js
	js/carousel.js
	js/collapse.js
	js/dropdown.js
	js/modal.js
	js/popover.js
	js/scrollspy.js
	js/tab.js
	js/tests/unit/affix.js
	js/tests/unit/button.js
	js/tests/unit/carousel.js
	js/tests/unit/modal.js
	js/tests/unit/tooltip.js
	js/tests/visual/modal.html
	js/tooltip.js
	less/component-animations.less
	less/jumbotron.less
	less/mixins/background-variant.less
	less/mixins/buttons.less
	less/mixins/responsive-visibility.less
	less/mixins/text-emphasis.less
	less/navbar.less
	less/navs.less
	less/scaffolding.less
	less/tooltip.less
	less/utilities.less
	less/variables.less
	package.json
	scss/_buttons.scss
	scss/_forms.scss
	scss/_modal.scss

js/tests/visual/collapse.html

@@ -19,7 +19,7 @@
     <div class="panel panel-default">
       <div class="panel-heading">
         <h4 class="panel-title">
-          <a data-toggle="collapse" data-parent="#accordion" href="#collapseOne">
+          <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseOne">
             Collapsible Group Item #1
           </a>
         </h4>
@@ -33,7 +33,7 @@
     <div class="panel panel-default">
       <div class="panel-heading">
         <h4 class="panel-title">
-          <a data-toggle="collapse" data-parent="#accordion" href="#collapseTwo">
+          <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseTwo">
             Collapsible Group Item #2
           </a>
         </h4>
@@ -47,7 +47,7 @@
     <div class="panel panel-default">
       <div class="panel-heading">
         <h4 class="panel-title">
-          <a data-toggle="collapse" data-parent="#accordion" href="#collapseThree">
+          <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseThree">
             Collapsible Group Item #3
           </a>
         </h4>