Cause Request.Socket.open to check `/etc/hosts` as well as DNS

when resolving hostnames.

During development, it can be useful to add entries to `/etc/hosts`
in the Docker container (to test ActivityPub federation, e.g.).
The Socket implementation in Request currently ignores `/etc/hosts`,
and only consults DNS. This patch changes that.

app/lib/request.rb

@@ -267,8 +267,9 @@ class Request
           Resolv::DNS.open do |dns|
             dns.timeouts = 5
             addresses = dns.getaddresses(host)
-            addresses = addresses.filter { |addr| addr.is_a?(Resolv::IPv6) }.take(2) + addresses.filter { |addr| !addr.is_a?(Resolv::IPv6) }.take(2)
           end
+          addresses.concat(Resolv::Hosts.new().getaddresses(host))
+          addresses = addresses.filter { |addr| addr.is_a?(Resolv::IPv6) }.take(2) + addresses.filter { |addr| !addr.is_a?(Resolv::IPv6) }.take(2)
         end
 
         socks = []