Bump bootstrap from 4.0.0 to 4.3.1

Bumps [bootstrap](https://github.com/twbs/bootstrap-rubygem) from 4.0.0 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...v4.3.1)

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

Author: dependabot[bot]

Gemfile

@@ -12,7 +12,7 @@ gem 'coffee-rails', '~> 4.2'
 gem 'turbolinks', '~> 5'
 gem 'jbuilder', '~> 2.5'
 gem 'bootsnap', '>= 1.1.0', require: false
-gem 'bootstrap', '~> 4.0.0.alpha6'
+gem 'bootstrap', '~> 4.3.1'
 gem 'devise', '~> 4.7', '>= 4.7.2'
 gem 'friendly_id', '~> 5.3'
 gem 'hirb', '~> 0.7.3'

Gemfile.lock

@@ -73,10 +73,10 @@ GEM
     bindex (0.8.1)
     bootsnap (1.5.1)
       msgpack (~> 1.0)
-    bootstrap (4.0.0)
-      autoprefixer-rails (>= 6.0.3)
-      popper_js (>= 1.12.9, < 2)
-      sass (>= 3.5.2)
+    bootstrap (4.3.1)
+      autoprefixer-rails (>= 9.1.0)
+      popper_js (>= 1.14.3, < 2)
+      sassc-rails (>= 2.0.0)
     builder (3.2.4)
     byebug (11.1.3)
     carrierwave (2.1.0)
@@ -233,6 +233,14 @@ GEM
       sprockets (>= 2.8, < 4.0)
       sprockets-rails (>= 2.0, < 4.0)
       tilt (>= 1.1, < 3)
+    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
     spring (2.1.1)
     spring-watcher-listen (2.0.1)
       listen (>= 2.7, < 4.0)
@@ -271,7 +279,7 @@ PLATFORMS
 DEPENDENCIES
   Smith_View_Tool!
   bootsnap (>= 1.1.0)
-  bootstrap (~> 4.0.0.alpha6)
+  bootstrap (~> 4.3.1)
   byebug
   carrierwave (~> 2.1)
   carrierwave-aws (~> 1.5)