Fix type error when modifying pauli coefficient in observable calibration.

[kylegulshen]

Description

PyQuil recently added a new check in the hash function that the pauil coefficients are complex. In calibrate_observables we set the coefficient of each observable in a list to equal one, then cast this list into a set which calls the hash function with the new check. We need to explicitly type one as a complex number when setting the coefficient.

These changes will need to be combined with #206 in order for the full build to pass. Furthermore, there appears to be a compiler timeout error in the ripple carry adder tests, possibly related to quil-lang/quilc#559

[jlapeyre]

LGTM too.

[jlapeyre]

EDIT: Wait, I just found #205, which explains what's going on.

I find two errors in the semaphoreci output:
pkg_resources.VersionConflict: (coverage 5.0.3 (/home/runner/.pyenv/3.6/lib/python3.6/site-packages), Requirement.parse('coverage<5'))
And
pluggy.manager.PluginValidationError: Plugin 'nbval' could not be loaded: (coverage 5.0.3 (/home/runner/.pyenv/3.6/lib/python3.6/site-packages), Requirement.parse('coverage<5'))!

Any idea what this means ? Does nbval require coverage version < 5 ?