Increase the timeout for switch to frame to avoid intermittent failures on travis

This is designed to fix failures such as that below. Through extra debugging and full logs on travis, it appears that sometimes getting `self.current_url` in `wait_for_correct_document` can take > 5s. My believe is that the browser is still loading, and loading the page is just being slow.

This extends the timeout to cover the slow case and seems to fix the issues.

```
======================================================================
ERROR: test_text_chat (test_MultipleBrowsers.MultipleBrowsersTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/travis/build/mozilla/talkilla/test/functional/test_MultipleBrowsers.py", line 130, in test_text_chat
self.bob.signin()
File "/home/travis/build/mozilla/talkilla/test/functional/driver.py", line 49, in signin
self.switchToSidebar()
File "/home/travis/build/mozilla/talkilla/test/functional/driver.py", line 164, in switchToSidebar
BASE_APP_URL + "/sidebar.html")
File "/home/travis/build/mozilla/talkilla/test/functional/driver.py", line 153, in switchToFrame
wait_for_correct_document, message=msg)
File "/home/travis/build/mozilla/talkilla/.venv/local/lib/python2.7/site-packages/selenium/webdriver/support/wait.py", line 71, in until
raise TimeoutException(message)
TimeoutException: Message: u'timed out waiting for //#social-sidebar-browser to be http://localhost:3000/sidebar.html after 5s seconds'
```