Update WordPressKit & WordPressAuthenticator to use the latest versions

[mindgraffiti]

Fixes # n/a

To test:

1. rake dependencies
2. run & build the app
3. Navigate to a site
4. Set Network Link Conditioner to 100% Loss
5. Navigate to Activity
6. If testing in Xcode, set a breakpoint in ActivityServiceRemote, L49
7. If testing on a device, check the app log for this message:

Check the console.log or app log for NSLocalizedDescription=The request timed out., NSErrorFailingURLStringKey=https://public-api.wordpress.com/wpcom/v2/sites/70760568/activity?_locale=en&number=1000&page=1, NSErrorFailingURLKey=https://public-api.wordpress.com/wpcom/v2/sites/{site_id}/activity?_locale=en&number=1000&page=1, _kCFStreamErrorDomainKey=4

Do not merge until:

1. WordPressKit PR has been merged Migrate to Swift 5 WordPressKit-iOS#232 ✔️
2. WordPressKit has the newly published release, 4.6.0-beta.6 ✔️
3. Authenticator PR has been merged Update version of WordPressKit to 4.6.0-beta.6 WordPressAuthenticator-iOS#201 ✔️
4. Authenticator has the newly published release, 1.11.0-beta.6 ✔️
5. The podfile has been updated to WordPressKit 4.6.0-beta.6 and Authenticator 1.11.0-beta.6 ✔️
6. The NSURL+IDN pod changes have been merged Update NSURL+IDN version to 0.4 #13644

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger an installable build for these changes by visiting CircleCI here.

[ScoutHarris]

✅ rake dependencies
✅ run & build the app
✅ If testing in Xcode, set a breakpoint in ActivityServiceRemote, L49
✅ Unit Tests

[Gio2018]

Did steps 1-6 and all worked. Looks very good!!