Beautify _config.yml.

See the non-whitespace diff https://github.com/twbs/bootstrap/pull/23448/files?w=1.

_config.yml

 # Dependencies
-markdown:         kramdown
-highlighter:      rouge
+markdown:       kramdown
+highlighter:    rouge
 
 kramdown:
-  auto_ids: true
+  auto_ids:     true
 
 # Permalinks
-permalink:        pretty
+permalink:      pretty
 
 # Server
-source:           .
-destination:      ./_gh_pages
-port:             9001
-baseurl:          ""
-url:              https://getbootstrap.com
-encoding:         UTF-8
-exclude:          [.git, .github, assets/scss/, build, js, node_modules, nuget, scss, vendor, bower.json, composer.json, Gemfile, Gemfile.lock, Gruntfile.js, package.js, package.json, package-lock.json, sache.json]
+source:         "."
+destination:    ./_gh_pages
+port:           9001
+baseurl:        ""
+url:            "https://getbootstrap.com"
+encoding:       UTF-8
+exclude:
+  - .git
+  - .github
+  - assets/scss/
+  - build
+  - js
+  - node_modules
+  - nuget
+  - scss
+  - vendor
+  - bower.json
+  - composer.json
+  - Gemfile
+  - Gemfile.lock
+  - Gruntfile.js
+  - package.js
+  - package.json
+  - package-lock.json
+  - sache.json
 
 plugins:
   - jekyll-redirect-from
@@ -23,35 +41,34 @@ plugins:
   - jekyll-toc
 
 # Social
-title: Bootstrap
-description: The most popular HTML, CSS, and JS library in the world.
-twitter: getbootstrap
-authors: Mark Otto, Jacob Thornton, and Bootstrap contributors
-social_logo_path: /assets/brand/bootstrap-social-logo.png
-social_image_path: /assets/brand/bootstrap-social.png
-
-# Custom vars
-current_version:  4.0.0-beta
-docs_version:     4.0
-repo:             https://github.com/twbs/bootstrap
-slack:            https://bootstrap-slack.herokuapp.com
+title:              Bootstrap
+description:        "The most popular HTML, CSS, and JS library in the world."
+twitter:            getbootstrap
+authors:            "Mark Otto, Jacob Thornton, and Bootstrap contributors"
+social_image_path:  /assets/brand/bootstrap-social.png
+social_logo_path:   /assets/brand/bootstrap-social-logo.png
 
+# Custom variables
+current_version:    4.0.0-beta
+docs_version:       4.0
+repo:               "https://github.com/twbs/bootstrap"
+slack:              "https://bootstrap-slack.herokuapp.com"
 download:
-  source:         https://github.com/twbs/bootstrap/archive/v4.0.0-beta.zip
-  dist:           https://github.com/twbs/bootstrap/releases/download/v4.0.0-beta/bootstrap-4.0.0-beta-dist.zip
+  source:           "https://github.com/twbs/bootstrap/archive/v4.0.0-beta.zip"
+  dist:             "https://github.com/twbs/bootstrap/releases/download/v4.0.0-beta/bootstrap-4.0.0-beta-dist.zip"
 
-blog:             https://blog.getbootstrap.com
-expo:             https://expo.getbootstrap.com
-themes:           https://themes.getbootstrap.com
-jobs:             https://jobs.getbootstrap.com
+blog:               "https://blog.getbootstrap.com"
+expo:               "https://expo.getbootstrap.com"
+jobs:               "https://jobs.getbootstrap.com"
+themes:             "https://themes.getbootstrap.com"
 
 cdn:
   # See https://www.srihash.org for info on how to generate the hashes
-  css:            https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css
-  css_hash:       "sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M"
-  js:             https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/js/bootstrap.min.js
-  js_hash:        "sha384-h0AbiXch4ZDo7tp9hKZ4TsHbi047NrKGLO3SEJAg45jXxnGIfYzk4Si90RDIqNm1"
-  jquery:         https://code.jquery.com/jquery-3.2.1.slim.min.js
-  jquery_hash:    "sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN"
-  popper:         https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js
-  popper_hash:    "sha384-b/U6ypiBEHpOf/4+1nzFpr53nxSS+GLCkfwBdFNTxtclqqenISfwAzpKaMNFNmj4"
+  css:              "https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css"
+  css_hash:         "sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M"
+  js:               "https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/js/bootstrap.min.js"
+  js_hash:          "sha384-h0AbiXch4ZDo7tp9hKZ4TsHbi047NrKGLO3SEJAg45jXxnGIfYzk4Si90RDIqNm1"
+  jquery:           "https://code.jquery.com/jquery-3.2.1.slim.min.js"
+  jquery_hash:      "sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN"
+  popper:           "https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js"
+  popper_hash:      "sha384-b/U6ypiBEHpOf/4+1nzFpr53nxSS+GLCkfwBdFNTxtclqqenISfwAzpKaMNFNmj4"