change cssutils version to fix py2.7 install

Currently on py2.7 Sentry will install, but when you do `sentry upgrade` or `sentry start` it will complain like this and not work:

```
File "/home/ronald/sentry/local/lib/python2.7/site-packages/cssutils-0.9.10-py2.7.egg/cssutils/helper.py", line 9, in <module>
    import urllib.request, urllib.parse, urllib.error
ImportError: No module named request
```

This is related to this bug: https://bitbucket.org/cthedot/cssutils/issue/29/python-27-release-egg-for-0910-has-python

Fixing the version of cssutils to <0.9.10 will install 0.9.10b1 which is not affected by the issue.