`fork` should fetch from the same "origin" Github URL.

features/fork.feature

@@ -17,6 +17,20 @@ Feature: hub fork
     And "git remote set-url mislav git@github.com:mislav/dotfiles.git" should be run
     And the url for "mislav" should be "git@github.com:mislav/dotfiles.git"
 
+  Scenario: Fork the repository when origin URL is private
+    Given the "origin" remote has url "git@github.com:evilchelu/dotfiles.git"
+    Given the GitHub API server:
+      """
+      before { halt 401 unless request.env['HTTP_AUTHORIZATION'] == 'token OTOKEN' }
+      get('/repos/mislav/dotfiles', :host_name => 'api.github.com') { 404 }
+      post('/repos/evilchelu/dotfiles/forks', :host_name => 'api.github.com') { '' }
+      """
+    When I successfully run `hub fork`
+    Then the output should contain exactly "new remote: mislav\n"
+    And "git remote add -f mislav ssh://git@github.com/evilchelu/dotfiles.git" should be run
+    And "git remote set-url mislav git@github.com:mislav/dotfiles.git" should be run
+    And the url for "mislav" should be "git@github.com:mislav/dotfiles.git"
+
   Scenario: --no-remote
     Given the GitHub API server:
       """

lib/hub/commands.rb

@@ -556,8 +556,9 @@ module Hub
       if args.include?('--no-remote')
         exit
       else
+        origin_url = project.remote.github_url
         url = forked_project.git_url(:private => true, :https => https_protocol?)
-        args.replace %W"remote add -f #{forked_project.owner} #{project.git_url}"
+        args.replace %W"remote add -f #{forked_project.owner} #{origin_url}"
         args.after %W"remote set-url #{forked_project.owner} #{url}"
         args.after 'echo', ['new remote:', forked_project.owner]
       end

lib/hub/context.rb

@@ -397,6 +397,10 @@ module Hub
         nil
       end
 
+      def github_url
+        urls.detect {|url| local_repo.known_host?(url.host) }
+      end
+
       def urls
         @urls ||= raw_urls.map do |url|
           with_normalized_url(url) do |normalized|