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: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -5,7 +5,7 @@
     "dev": "gulp watch"
   },
   "devDependencies": {
-    "bootstrap-sass": "^3.3.7",
+    "bootstrap-sass": "^3.4.3",
     "gulp": "^3.9.1",
     "jquery": "^3.1.0",
     "laravel-elixir": "^6.0.0-14",