Bump bootstrap from 4.1.1 to 4.3.1

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 4.1.1 to 4.3.1.
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](twbs/bootstrap@v4.1.1...v4.3.1)

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

Author: dependabot[bot]

package-lock.json

@@ -14,7 +14,7 @@
     "@angular/platform-browser-dynamic": "~7.1.0",
     "@angular/router": "~7.1.0",
     "@ng-bootstrap/ng-bootstrap": "^5.1.2",
-    "bootstrap": "4.1.1",
+    "bootstrap": "4.3.1",
     "core-js": "^2.5.4",
     "ngx-bootstrap": "^5.3.1",
     "rxjs": "~6.3.3",