Thanks to the chrono update, we no longer include an
obsolete/vulnerable version of the `time` crate. Unfortunately, it
turns out that chrono has the same trouble as `time`: it, too, looks
at the environment via localtime_r, and the environment isn't
threadsafe.
One step forward, one step back. At least the underlying issue is
one that lots of people seem to care about; let's hope they come up
with a solution.