The interim git ref carried Predicator.Simple while it was
unreleased. predicator 9.2.0 carries it, so the dependency goes
back to a hex requirement at `~> 9.2`.

The floor moves from 9.1 to 9.2: Predicator.Simple and its
per-value-kind operators/1 landed there, and StatifierUI.Expression
reads both. The comment keeps the standing reason predicator is
declared here directly rather than left to arrive through statifier,
and drops the paragraph describing the pin.

mix hex.build refuses a git dependency, so this is what makes the
cut 0.4.0 publishable.

Refs: sui-0m3