Bump bootstrap-sass from 3.3.7 to 3.4.0 (#443)

Bumps [bootstrap-sass](https://github.com/twbs/bootstrap-sass) from 3.3.7 to 3.4.0.
- [Release notes](https://github.com/twbs/bootstrap-sass/releases)
- [Changelog](https://github.com/twbs/bootstrap-sass/blob/master/CHANGELOG.md)
- [Commits](twbs/bootstrap-sass@v3.3.7...v3.4.0)

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

Gemfile

@@ -13,7 +13,7 @@ gem 'activeadmin'
 gem 'api-pagination'
 gem 'attachinary'
 gem 'autoprefixer-rails'
-gem 'bootstrap-sass', '~> 3.3.5'
+gem 'bootstrap-sass', '~> 3.4.0'
 gem 'central-support', github: 'Codeminer42/cm42-central-support', require: 'central/support'
 gem 'chartkick'
 gem 'chronic'

Gemfile.lock

@@ -93,9 +93,9 @@ GEM
       rack (>= 0.9.0)
     binding_of_caller (0.8.0)
       debug_inspector (>= 0.0.1)
-    bootstrap-sass (3.3.7)
+    bootstrap-sass (3.4.0)
       autoprefixer-rails (>= 5.2.1)
-      sass (>= 3.3.4)
+      sassc (>= 2.0.0)
     builder (3.2.3)
     bullet (5.9.0)
       activesupport (>= 3.0.0)
@@ -477,6 +477,9 @@ GEM
       sprockets (>= 2.8, < 4.0)
       sprockets-rails (>= 2.0, < 4.0)
       tilt (>= 1.1, < 3)
+    sassc (2.0.0)
+      ffi (~> 1.9.6)
+      rake
     shoulda-matchers (3.1.2)
       activesupport (>= 4.0.0)
     sidekiq (5.2.5)
@@ -558,7 +561,7 @@ DEPENDENCIES
   autoprefixer-rails
   better_errors
   binding_of_caller
-  bootstrap-sass (~> 3.3.5)
+  bootstrap-sass (~> 3.4.0)
   bullet
   capybara
   capybara-screenshot