Release Prolific Consolidator version 12.0.0.
Release Prolific Consolidator version 12.0.0.

 * Upgrade `staccato` to `^12.0.0`. Closes #1273.
 * Upgrade `proof` to `^9.0.1`. Closes #1272.
 * Update `LICENSE` for 2020. Closes #1271.
 * Merge branch `master`.
 * Removed unused member variable. Closes #1250.

Closes #1274.

bigeasy/prolific,bigeasy/prolific