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] <[email protected]>

Gemfile

@@ -47,7 +47,7 @@ gem 'graphql'
 gem 'bootsnap', '>= 1.1.0', require: false
 
 # bootstrap
-gem 'bootstrap', '~> 4.0.0'
+gem 'bootstrap', '~> 4.3.1'
 gem 'jquery-rails' # needed for bootstap ... 
 
 # pictures

Gemfile.lock

@@ -48,7 +48,7 @@ GEM
       sshkit (>= 1.6.1, != 1.7.0)
     arel (9.0.0)
     ast (2.4.1)
-    autoprefixer-rails (9.7.3)
+    autoprefixer-rails (10.1.0.0)
       execjs
     babel-source (5.8.35)
     babel-transpiler (0.7.0)
@@ -59,10 +59,10 @@ GEM
     bindex (0.8.1)
     bootsnap (1.4.5)
       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 (3.2.3)
     byebug (11.0.1)
     capistrano (3.14.1)
@@ -126,7 +126,7 @@ GEM
     faraday (0.17.1)
       multipart-post (>= 1.2, < 3)
     fastimage (2.1.7)
-    ffi (1.11.3)
+    ffi (1.14.2)
     font-awesome-rails (4.7.0.5)
       railties (>= 3.2, < 6.1)
     font-awesome-sass (5.12.0)
@@ -187,7 +187,7 @@ GEM
     parser (2.7.2.0)
       ast (~> 2.4.1)
     pg (1.1.4)
-    popper_js (1.14.5)
+    popper_js (1.16.0)
     pry (0.12.2)
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
@@ -232,8 +232,8 @@ GEM
       thor (>= 0.19.0, < 2.0)
     rainbow (3.0.0)
     rake (13.0.3)
-    rb-fsevent (0.10.3)
-    rb-inotify (0.10.0)
+    rb-fsevent (0.10.4)
+    rb-inotify (0.10.1)
       ffi (~> 1.0)
     react-rails (2.6.0)
       babel-transpiler (>= 0.7.0)
@@ -293,6 +293,12 @@ GEM
       tilt (>= 1.1, < 3)
     sassc (2.3.0)
       ffi (~> 1.9)
+    sassc-rails (2.1.2)
+      railties (>= 4.0.0)
+      sassc (>= 2.0)
+      sprockets (> 3.0)
+      sprockets-rails
+      tilt
     selenium-webdriver (3.142.6)
       childprocess (>= 0.5, < 4.0)
       rubyzip (>= 1.2.2)
@@ -384,7 +390,7 @@ PLATFORMS
 
 DEPENDENCIES
   bootsnap (>= 1.1.0)
-  bootstrap (~> 4.0.0)
+  bootstrap (~> 4.3.1)
   byebug
   capistrano (~> 3.10)
   capistrano-bundler (~> 2.0)