Merge branch 'master' into v4

Conflicts:
	.travis.yml
	Gruntfile.js
	bower.json
	dist/css/bootstrap.css
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css
	dist/js/bootstrap.js
	dist/js/bootstrap.min.js
	docs/_data/glyphicons.yml
	docs/_includes/components/breadcrumbs.html
	docs/_includes/components/button-dropdowns.html
	docs/_includes/components/button-groups.html
	docs/_includes/components/dropdowns.html
	docs/_includes/components/glyphicons.html
	docs/_includes/components/labels.html
	docs/_includes/components/list-group.html
	docs/_includes/components/media.html
	docs/_includes/components/navs.html
	docs/_includes/components/panels.html
	docs/_includes/components/progress-bars.html
	docs/_includes/components/thumbnails.html
	docs/_includes/components/wells.html
	docs/_includes/css/buttons.html
	docs/_includes/css/forms.html
	docs/_includes/css/helpers.html
	docs/_includes/css/images.html
	docs/_includes/css/less.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/examples.html
	docs/_includes/getting-started/grunt.html
	docs/_includes/getting-started/license.html
	docs/_includes/getting-started/template.html
	docs/_includes/header.html
	docs/_includes/js/affix.html
	docs/_includes/js/alerts.html
	docs/_includes/js/carousel.html
	docs/_includes/js/collapse.html
	docs/_includes/js/dropdowns.html
	docs/_includes/js/modal.html
	docs/_includes/js/overview.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/_layouts/default.html
	docs/assets/css/docs.min.css
	docs/assets/css/src/docs.css
	docs/assets/js/customize.min.js
	docs/assets/js/docs.min.js
	docs/assets/js/raw-files.min.js
	docs/assets/js/vendor/FileSaver.js
	docs/assets/js/vendor/autoprefixer.js
	docs/assets/js/vendor/uglify.min.js
	docs/dist/css/bootstrap.css
	docs/dist/css/bootstrap.css.map
	docs/dist/css/bootstrap.min.css
	docs/dist/js/bootstrap.min.js
	docs/examples/blog/index.html
	docs/examples/carousel/index.html
	docs/examples/cover/index.html
	docs/examples/dashboard/index.html
	docs/examples/narrow-jumbotron/narrow-jumbotron.css
	docs/examples/navbar-fixed-top/index.html
	docs/examples/navbar-static-top/index.html
	docs/examples/non-responsive/index.html
	docs/examples/non-responsive/non-responsive.css
	docs/examples/theme/index.html
	grunt/configBridge.json
	js/affix.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/tooltip.js
	less/badges.less
	less/glyphicons.less
	less/type.less
	less/variables.less
	package.json
	scss/_dropdown.scss
	scss/_forms.scss
	test-infra/npm-shrinkwrap.json

docs/components/helpers.md

@@ -94,14 +94,14 @@ Set an element to `display: block;` and center via `margin`. Available as a mixi
 {% endexample %}
 
 {% highlight scss %}
-// Classes
+// Class
 .center-block {
   display: block;
   margin-left: auto;
   margin-right: auto;
 }
 
-// Usage as mixins
+// Usage as a mixin
 .element {
   @include center-block;
 }
@@ -126,7 +126,7 @@ Easily clear `float`s by adding `.clearfix` **to the parent element**. Utilizes
   }
 }
 
-// Usage as a Mixin
+// Usage as a mixin
 .element {
   @include clearfix;
 }
@@ -151,12 +151,12 @@ The `.invisible` class can be used to toggle only the visibility of an element,
 {% endhighlight %}
 
 {% highlight scss %}
-// Classes
+// Class
 .invisible {
   visibility: hidden;
 }
 
-// Usage as mixin
+// Usage as a mixin
 .element {
   .invisible();
 }
@@ -171,7 +171,7 @@ Hide an element to all devices **except screen readers** with `.sr-only`. Combin
 {% endhighlight %}
 
 {% highlight scss %}
-// Usage as a Mixin
+// Usage as a mixin
 .skip-navigation {
   @include sr-only;
   @include sr-only-focusable;
@@ -187,7 +187,7 @@ Utilize the `.text-hide` class or mixin to help replace an element's text conten
 {% endhighlight %}
 
 {% highlight scss %}
-// Usage as a Mixin
+// Usage as a mixin
 .heading {
   @include text-hide;
 }