fix(package): update bootstrap to version 4.3.1

Closes #28

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
   "main": "htdocs/index.html",
   "repository": "https://github.com/brainsware/sealas-site.git",
   "dependencies": {
-    "bootstrap": "^3.3.7",
+    "bootstrap": "^4.3.1",
     "highlight.js": "^9.12.0",
     "metalsmith-external-links": "^0.1.2",
     "nanoajax": "^0.4.3",