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

@@ -11,7 +11,7 @@ gem 'wdm', '~> 0.1.0', platforms: [:mswin, :mingw]
 gem 'tzinfo-data', '~> 1.2018', '>= 1.2018.4', platforms: [:mswin, :mingw]
 
 # Middleman Gems
-gem 'bootstrap', '~> 4.0.0.beta'
+gem 'bootstrap', '~> 4.3.1'
 gem 'middleman', '~> 4.3', '>= 4.3.5'
 gem 'middleman-compass', '~> 4.0', '>= 4.0.1'
 gem 'middleman-deploy', '~> 2.0.0.pre.alpha'

Gemfile.lock

@@ -1,20 +1,34 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    actionpack (5.0.7.2)
+      actionview (= 5.0.7.2)
+      activesupport (= 5.0.7.2)
+      rack (~> 2.0)
+      rack-test (~> 0.6.3)
+      rails-dom-testing (~> 2.0)
+      rails-html-sanitizer (~> 1.0, >= 1.0.2)
+    actionview (5.0.7.2)
+      activesupport (= 5.0.7.2)
+      builder (~> 3.1)
+      erubis (~> 2.7.0)
+      rails-dom-testing (~> 2.0)
+      rails-html-sanitizer (~> 1.0, >= 1.0.3)
     activesupport (5.0.7.2)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
     addressable (2.6.0)
       public_suffix (>= 2.0.2, < 4.0)
-    autoprefixer-rails (9.6.1)
+    autoprefixer-rails (9.7.0)
       execjs
     backports (3.15.0)
-    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 (3.2.3)
     chunky_png (1.3.11)
     coffee-script (2.4.1)
       coffee-script-source
@@ -34,6 +48,7 @@ GEM
       sass (>= 3.2, < 3.5)
     concurrent-ruby (1.1.5)
     contracts (0.13.0)
+    crass (1.0.5)
     dotenv (2.7.5)
     em-websocket (0.5.1)
       eventmachine (>= 0.12.9)
@@ -57,7 +72,11 @@ GEM
     listen (3.0.8)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
+    loofah (2.3.1)
+      crass (~> 1.0.2)
+      nokogiri (>= 1.5.9)
     memoist (0.16.0)
+    method_source (0.9.2)
     middleman (4.3.5)
       coffee-script (~> 2.2)
       haml (>= 4.0.5)
@@ -103,24 +122,40 @@ GEM
     middleman-sprockets (4.1.1)
       middleman-core (~> 4.0)
       sprockets (>= 3.0)
+    mini_portile2 (2.4.0)
     minitest (5.11.3)
     multi_json (1.13.1)
     net-sftp (2.1.2)
       net-ssh (>= 2.6.5)
     net-ssh (5.2.0)
+    nokogiri (1.10.4)
+      mini_portile2 (~> 2.4.0)
     padrino-helpers (0.13.3.4)
       i18n (~> 0.6, >= 0.6.7)
       padrino-support (= 0.13.3.4)
       tilt (>= 1.4.1, < 3)
     padrino-support (0.13.3.4)
       activesupport (>= 3.1)
     parallel (1.17.0)
-    popper_js (1.11.1)
+    popper_js (1.14.5)
     ptools (1.3.5)
     public_suffix (3.1.1)
     rack (2.0.7)
     rack-livereload (0.3.17)
       rack
+    rack-test (0.6.3)
+      rack (>= 1.0)
+    rails-dom-testing (2.0.3)
+      activesupport (>= 4.2.0)
+      nokogiri (>= 1.6)
+    rails-html-sanitizer (1.3.0)
+      loofah (~> 2.3)
+    railties (5.0.7.2)
+      actionpack (= 5.0.7.2)
+      activesupport (= 5.0.7.2)
+      method_source
+      rake (>= 0.8.7)
+      thor (>= 0.18.1, < 2.0)
     rake (12.3.3)
     rb-fsevent (0.10.3)
     rb-inotify (0.10.0)
@@ -129,13 +164,23 @@ GEM
     sassc (2.0.1)
       ffi (~> 1.9)
       rake
+    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 (3.2.1)
+      actionpack (>= 4.0)
+      activesupport (>= 4.0)
+      sprockets (>= 3.0.0)
     temple (0.8.1)
     thor (0.20.3)
     thread_safe (0.3.6)
@@ -149,7 +194,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  bootstrap (~> 4.0.0.beta)
+  bootstrap (~> 4.3.1)
   middleman (~> 4.3, >= 4.3.5)
   middleman-compass (~> 4.0, >= 4.0.1)
   middleman-deploy (~> 2.0.0.pre.alpha)