Changed deliverable to milestone

[kelleyb]

Apparently Richie forgot.

[kmcnellis]

I think the term "milestone" is a bit of a different connotation, and therefore needs explaining on what we expect a milestone to be. For instance, in github, a alpha or beta release could be considered a milestone, but we want discrete sets of features (not just a project getting to a certain point)

[kmcnellis]

Maybe add something like "Each milestone should be a overarching goal, consisting of a well-defined large-scale feature, and be able to be broken up into several issues."

[kelleyb]

Yeah, I'll add a bit explaining that.

[aeksco]

@kelleyb What's the status of this PR? I think the changes here are solid - we'll likely re-tool them a bit (as per @kmcnellis 's comment) during the summer as we prepare for the Fall 2018 semester. LMK your thoughts when you have a chance - thanks!