Running `servo-tidy` in a virtualenv where all you've done is `pip install servo-tidy==0.3.0` doesn't actually work because of missing dependencies. PyYAML and voluptuous are required as well. I don't know anything about python package management but declaring these missing dependencies seems like an appropriate thing to do. Patch itself is untested because I don't know how, although with these dependencies installed in my virtualenv running `servo-tidy` works.
- also update requriements "pyflakes" from 0.8 to 0.8.1 due to following issue
```
Traceback (most recent call last):
File "/Users/Askeing/software/servo/python/_virtualenv/bin/servo-tidy", line 5, in <module>
from pkg_resources import load_entry_point
File "/Users/Askeing/software/servo/python/_virtualenv/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3084, in <module>
@_call_aside
File "/Users/Askeing/software/servo/python/_virtualenv/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3070, in _call_aside
f(*args, **kwargs)
File "/Users/Askeing/software/servo/python/_virtualenv/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3097, in
_initialize_master_working_set
working_set = WorkingSet._build_master()
File "/Users/Askeing/software/servo/python/_virtualenv/lib/python2.7/site-packages/pkg_resources/__init__.py", line 653, in _build_master
return cls._build_from_requirements(__requires__)
File "/Users/Askeing/software/servo/python/_virtualenv/lib/python2.7/site-packages/pkg_resources/__init__.py", line 666, in
_build_from_requirements
dists = ws.resolve(reqs, Environment())
File "/Users/Askeing/software/servo/python/_virtualenv/lib/python2.7/site-packages/pkg_resources/__init__.py", line 839, in resolve
raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'pyflakes==0.8.1' distribution was not found and is required by servo-tidy
```
