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

nuget/bootstrap.nuspec

@@ -2,7 +2,7 @@
 <package xmlns="http://schemas.microsoft.com/packaging/2011/08/nuspec.xsd">
   <metadata>
     <id>bootstrap</id>
-    <version>4.1.0</version>
+    <version>4.2.0</version>
     <title>Bootstrap CSS</title>
     <authors>The Bootstrap Authors, Twitter Inc.</authors>
     <owners>bootstrap</owners>
@@ -11,7 +11,7 @@
     <summary>Bootstrap framework in CSS. Includes fonts and JavaScript</summary>
     <language>en-us</language>
     <projectUrl>https://getbootstrap.com/</projectUrl>
-    <iconUrl>https://getbootstrap.com/docs/4.1/assets/img/favicons/apple-touch-icon.png</iconUrl>
+    <iconUrl>https://getbootstrap.com/docs/4.2/assets/img/favicons/apple-touch-icon.png</iconUrl>
     <licenseUrl>https://github.com/twbs/bootstrap/blob/master/LICENSE</licenseUrl>
     <copyright>Copyright 2017-2018</copyright>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>