tox: Update requests to 2.9.0.

Minor Improvements (Backwards compatible)

- The verify keyword argument now supports being passed a path to a directory
  of CA certificates, not just a single-file bundle.
- Warnings are now emitted when sending files opened in text mode.
- Added the 511 Network Authentication Required status code to the status code
  registry.

Bugfixes

- For file-like objects that are not seeked to the very beginning, we now send
  the content length for the number of bytes we will actually read, rather than
  the total size of the file, allowing partial file uploads.
- When uploading file-like objects, if they are empty or have no obvious
  content length we set Transfer-Encoding: chunked rather than
  Content-Length: 0.
- We correctly receive the response in buffered mode when uploading chunked
  bodies.
- We now handle being passed a query string as a bytestring on Python 3, by
  decoding it as UTF-8.
- Sessions are now closed in all cases (exceptional and not) when using the
  functional API rather than leaking and waiting for the garbage collector to
  clean them up.
- Correctly handle digest auth headers with a malformed qop directive that
  contains no token, by treating it the same as if no qop directive was
  provided at all.
- Minor performance improvements when removing specific cookies by name.

tox.ini

@@ -107,7 +107,7 @@ deps =
     {[testenv:misc]deps}
     astroid==1.4.1
     pylint==1.5.1
-    requests==2.8.1
+    requests==2.9.0
 commands =
     {envpython} scripts/link_pyqt.py --tox {envdir}
     {envpython} -m pylint scripts qutebrowser --output-format=colorized --reports=no