Fixed issue with lein-parent projects and managed-dependencies

[joshuaeckroth]

vizdeps would crash when using managed-dependencies in a parent project due to a missing version in the root project.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[hlship]

I'll be pleased to look at this, once the CLA is signed. Thanks so much!