Error installing with pip

## Bug report
I am trying to install moldesign through pip, but I receive an error stating that nbmolviz 0.7.0 has requirement moldesign>=0.8rc1, which I believe is the development version? If so, it seems that maybe nbmolviz is prematurely assuming the next version of moldesign and in the process is breaking the version currently available through pip. Any help getting past this issue so that I can successfully set up moldesign 0.7.3 would be greatly appreciated. Thanks! (errors from pip included below)
#### Description

#### Steps to reproduce

pip2 install --user moldesign

Here is the portion of the output containing the error:

nbmolviz 0.7.0 has requirement moldesign>=0.8rc1, but you'll have moldesign 0.7.3 which is incompatible.

#### Environment
- Operating system: Ubuntu 16.04
- `python --version` output: 2.7.12
- `pip show moldesign nbmolviz | grep -B1 Version` output:
Name: moldesign
Version: 0.7.3
--
Name: nbmolviz
Version: 0.7.0

Start by reproducing `pip2 install --user moldesign` in the reported Ubuntu 16.04/Python 2.7 environment and inspect the dependency metadata for nbmolviz 0.7.0 and moldesign 0.7.3. Done means the documented installation completes without the reported version conflict.

Written by the indexing model from the issue text.