Bump bootstrap-sass from 3.3.7 to 3.4.3

Bumps [bootstrap-sass](https://github.com/twbs/bootstrap-sass) from 3.3.7 to 3.4.3.
- [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...v3.4.3)

---
updated-dependencies:
- dependency-name: bootstrap-sass
  dependency-type: indirect
...

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

yarn.lock

@@ -1497,8 +1497,8 @@ boolbase@^1.0.0:
   resolved "https://registry.yarnpkg.com/boolbase/-/boolbase-1.0.0.tgz#68dff5fbe60c51eb37725ea9e3ed310dcc1e776e"
 
 bootstrap-sass@^3.3.7:
-  version "3.3.7"
-  resolved "https://registry.yarnpkg.com/bootstrap-sass/-/bootstrap-sass-3.3.7.tgz#6596c7ab40f6637393323ab0bc80d064fc630498"
+  version "3.4.3"
+  resolved "https://registry.yarnpkg.com/bootstrap-sass/-/bootstrap-sass-3.4.3.tgz#742cc8f4286303ae9fe8e4c95237321eae73766c"
 
 brace-expansion@^1.1.7:
   version "1.1.8"