Bump bootstrap from 4.2.1 to 4.3.1

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 4.2.1 to 4.3.1.
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](twbs/bootstrap@v4.2.1...v4.3.1)

---
updated-dependencies:
- dependency-name: bootstrap
  dependency-type: direct:production
...

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

Author: dependabot[bot]

package-lock.json

@@ -21,7 +21,7 @@
   },
   "dependencies": {
     "ajv": "^6.7.0",
-    "bootstrap": ">=4.1.2",
+    "bootstrap": ">=4.3.1",
     "hoek": "^4.2.1",
     "popper.js": "^1.14.6",
     "startbootstrap-agency": "^4.1.1"