Fix secure.travis-ci.org redirect

`fullpath` starts with SCRIPT_NAME. From the Rack spec:

> The SCRIPT_NAME, if non-empty, must start with /

Fixes travis-ci/travis-ci#1278.

config.ru

@@ -9,7 +9,7 @@ class RedirectSubdomain < Struct.new(:app, :from)
   def call(env)
     request = Rack::Request.new(env)
     if request.host == from
-      [301, { 'Location' => "https://travis-ci.org/#{request.fullpath}", 'Content-Type' => 'text/html' }, []]
+      [301, { 'Location' => "https://travis-ci.org#{request.fullpath}", 'Content-Type' => 'text/html' }, []]
     else
       app.call(env)
     end