Use PyQuil v4

[jselig-rigetti]

Update the pyquil dependency to use v4.

Note that there's no official v4 release as of yet, but based on https://github.com/rigetti/pyquil/milestone/27 the rc releases should be stable with the eventual release.

[isaacdevlugt]

Hey @jselig-rigetti! Is this something that you or someone else at Rigetti would be interested in making a contribution for?

[jselig-rigetti]

Yes, I plan to take it on, you could assign it to me 👍

[isaacdevlugt]

Awesome! Let us know if you have any questions or concerns 😄

[jselig-rigetti]

Blocked by #147