Bump bootstrap from 4.0.0.beta to 4.3.1

Bumps [bootstrap](https://github.com/twbs/bootstrap-rubygem) from 4.0.0.beta to 4.3.1.
- [Release notes](https://github.com/twbs/bootstrap-rubygem/releases)
- [Changelog](https://github.com/twbs/bootstrap-rubygem/blob/master/CHANGELOG.md)
- [Commits](twbs/bootstrap-rubygem@v4.0.0.beta...v4.3.1)

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile

@@ -13,7 +13,7 @@ gem 'tzinfo-data', '~> 1.2018', '>= 1.2018.4', platforms: [:mswin, :mingw]
 # Middleman Gems
 gem 'middleman', '~> 4.4'
 gem 'middleman-core', '~> 4.4'
-gem 'bootstrap', '~> 4.0.0.beta'
+gem 'bootstrap', '~> 4.3.1'
 gem 'middleman-compass', '~> 4.0', '>= 4.0.1'
 gem 'middleman-deploy', '~> 2.0.0.pre.alpha'
 gem 'middleman-livereload', '~> 3.4', '>= 3.4.6'

Gemfile.lock

@@ -1,6 +1,19 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    actionpack (6.1.3.2)
+      actionview (= 6.1.3.2)
+      activesupport (= 6.1.3.2)
+      rack (~> 2.0, >= 2.0.9)
+      rack-test (>= 0.6.3)
+      rails-dom-testing (~> 2.0)
+      rails-html-sanitizer (~> 1.0, >= 1.2.0)
+    actionview (6.1.3.2)
+      activesupport (= 6.1.3.2)
+      builder (~> 3.1)
+      erubi (~> 1.4)
+      rails-dom-testing (~> 2.0)
+      rails-html-sanitizer (~> 1.1, >= 1.2.0)
     activesupport (6.1.3.2)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 1.6, < 2)
@@ -9,13 +22,14 @@ GEM
       zeitwerk (~> 2.3)
     addressable (2.7.0)
       public_suffix (>= 2.0.2, < 5.0)
-    autoprefixer-rails (9.6.1)
-      execjs
+    autoprefixer-rails (10.2.5.1)
+      execjs (> 0)
     backports (3.21.0)
-    bootstrap (4.0.0.beta)
-      autoprefixer-rails (>= 6.0.3)
-      popper_js (~> 1.11.1)
-      sass (>= 3.4.19)
+    bootstrap (4.3.1)
+      autoprefixer-rails (>= 9.1.0)
+      popper_js (>= 1.14.3, < 2)
+      sassc-rails (>= 2.0.0)
+    builder (3.2.4)
     chunky_png (1.3.11)
     coffee-script (2.4.1)
       coffee-script-source
@@ -35,10 +49,12 @@ GEM
       sass (>= 3.2, < 3.5)
     concurrent-ruby (1.1.9)
     contracts (0.13.0)
+    crass (1.0.6)
     dotenv (2.7.6)
     em-websocket (0.5.1)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
+    erubi (1.10.0)
     erubis (2.7.0)
     eventmachine (1.2.7)
     execjs (2.8.1)
@@ -59,7 +75,11 @@ GEM
     listen (3.0.8)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
+    loofah (2.10.0)
+      crass (~> 1.0.2)
+      nokogiri (>= 1.5.9)
     memoist (0.16.2)
+    method_source (1.0.0)
     middleman (4.4.0)
       coffee-script (~> 2.2)
       haml (>= 4.0.5)
@@ -107,38 +127,67 @@ GEM
     middleman-sprockets (4.1.1)
       middleman-core (~> 4.0)
       sprockets (>= 3.0)
+    mini_portile2 (2.5.3)
     minitest (5.14.4)
     multi_json (1.13.1)
     net-sftp (2.1.2)
       net-ssh (>= 2.6.5)
     net-ssh (5.2.0)
+    nokogiri (1.11.7)
+      mini_portile2 (~> 2.5.0)
+      racc (~> 1.4)
     padrino-helpers (0.15.1)
       i18n (>= 0.6.7, < 2)
       padrino-support (= 0.15.1)
       tilt (>= 1.4.1, < 3)
     padrino-support (0.15.1)
     parallel (1.20.1)
     parslet (2.0.0)
-    popper_js (1.11.1)
+    popper_js (1.16.0)
     ptools (1.3.5)
     public_suffix (4.0.6)
+    racc (1.5.2)
     rack (2.2.3)
     rack-livereload (0.3.17)
       rack
+    rack-test (1.1.0)
+      rack (>= 1.0, < 3)
+    rails-dom-testing (2.0.3)
+      activesupport (>= 4.2.0)
+      nokogiri (>= 1.6)
+    rails-html-sanitizer (1.3.0)
+      loofah (~> 2.3)
+    railties (6.1.3.2)
+      actionpack (= 6.1.3.2)
+      activesupport (= 6.1.3.2)
+      method_source
+      rake (>= 0.8.7)
+      thor (~> 1.0)
+    rake (13.0.3)
     rb-fsevent (0.11.0)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     rexml (3.2.5)
     sass (3.4.25)
     sassc (2.4.0)
       ffi (~> 1.9)
+    sassc-rails (2.1.2)
+      railties (>= 4.0.0)
+      sassc (>= 2.0)
+      sprockets (> 3.0)
+      sprockets-rails
+      tilt
     servolux (0.13.0)
     slim (3.0.9)
       temple (>= 0.7.6, < 0.9)
       tilt (>= 1.3.3, < 2.1)
     sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
+    sprockets-rails (3.2.2)
+      actionpack (>= 4.0)
+      activesupport (>= 4.0)
+      sprockets (>= 3.0.0)
     temple (0.8.1)
     thor (1.1.0)
     tilt (2.0.10)
@@ -155,7 +204,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  bootstrap (~> 4.0.0.beta)
+  bootstrap (~> 4.3.1)
   middleman (~> 4.4)
   middleman-compass (~> 4.0, >= 4.0.1)
   middleman-core (~> 4.4)