Prep for v4.2.0 release

- Move 4.1 docs to 4.2
- Update versions everywhere to 4.1.3 with release script
- Manually bump the shorthand version in package.json
- Add 4.2 to the versions docs page
- Update some redirects
- Fix tests asset URLs
- Bump Nuget and more

package.json

@@ -1,8 +1,8 @@
 {
   "name": "bootstrap",
   "description": "The most popular front-end framework for developing responsive, mobile first projects on the web.",
-  "version": "4.1.3",
-  "version_short": "4.1",
+  "version": "4.2.0",
+  "version_short": "4.2",
   "keywords": [
     "css",
     "sass",