[Security] Bump bootstrap from 3.4.1 to 4.1.2

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 3.4.1 to 4.1.2. **This update includes security fixes.**
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](twbs/bootstrap@v3.4.1...v4.1.2)

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

Author: dependabot-support

package-lock.json

@@ -23,7 +23,7 @@
     "url": "https://github.com/publiclab/inline-markdown-editor/issues"
   },
   "dependencies": {
-    "bootstrap": "~3.4.0",
+    "bootstrap": "~4.1.2",
     "font-awesome": "~4.7.0",
     "jquery": "~3",
     "megamark": "^3.2.2",