docker run example in README does not work for me

```
(clodius) clodius$ curl https://raw.githubusercontent.com/hms-dbmi/clodius/develop/test/sample_data/geneAnnotationsExonsUnions.short.bed \
> /tmp/clodius/input/sample.short.bed

(clodius) clodius$ docker stop clodius
Error response from daemon: No such container: clodius

(clodius) clodius$ docker pull gehlenborglab/clodius
Using default tag: latest
latest: Pulling from gehlenborglab/clodius
....
Digest: sha256:69c09cc20bdfa0d102a7888d502713a9cd0e16fb9637250dd5f6bdb3dc5c1ef3
Status: Downloaded newer image for gehlenborglab/clodius:latest

(clodius) clodius$ docker run -v /tmp/clodius/input:/tmp/ \
> gehlenborglab/clodius \
> clodius aggregate bigwig /tmp/file.bigwig
Traceback (most recent call last):
File "/usr/local/bin/clodius", line 11, in
load_entry_point('clodius==0.9.4', 'console_scripts', 'clodius')()
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 764, in __call__
return self.main(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 717, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 1137, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 1137, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 956, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 555, in invoke
return callback(*args, **kwargs)
File "build/bdist.linux-x86_64/egg/clodius/cli/aggregate.py", line 1372, in bigwig
NameError: global name '_bigwig' is not defined
```