Don't block access to content from `/.well-known/`

The `/.well-known/` directory represents the standard path prefix
for "well-known locations" (e.g.: `/.well-known/manifest.json`,
`/.well-known/keybase.txt`), and therefore, access to its visible
content should not be blocked.

Ref: http://tools.ietf.org/html/rfc5785
     https://www.mnot.net/blog/2010/04/07/well-known

Close h5bp/server-configs-apache#31.