Fix .htaccess issue with subdomain

[edent]

Fixes #419

Proposed changes:

• Blogs in subdirectories didn't work with the previous .htaccess rule

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

• Create a blog in a subdirectory - for example example.com/blog/
• Try to use the original .htaccess file
• Note that visiting https://example.com/.well-known/webfinger gets redirected to https://blog///.well-knownwebfinger
• Try this new, improved, organic, fat free, low-sugar .htaccess file
• Rejoice as you are redirected correctly.

[pfefferle]

LGTM