use Capybara.using_session method for multiple browsers specs

spec/sessions_helper.rb

@@ -1,8 +1,3 @@
-def in_browser(name)
+def in_browser(name, &block)
-  old_session = Capybara.session_name
+  Capybara.using_session(name, &block)
-
-  Capybara.session_name = name
-  yield
-
-  Capybara.session_name = old_session
 end