Fixes ParseRequirement error with latest pip

[r4ghu]

While trying to execute the following command - pip install git+https://github.com/mattloper/chumpy.git. I am receiving the following error -

File "/private/var/folders/65/r762fpy14s15_v7759ltbvs00000gn/T/pip-req-build-3hgeg5w5/setup.py", line 15, in <listcomp>
        install_requires = [str(ir.req) for ir in install_reqs]
    AttributeError: 'ParsedRequirement' object has no attribute 'req'
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

The current PR fixes this issue.

[mattloper]

Thanks! I merged a similar PR that does the same thing, so I think we're all set on this.