rename sweet_potato_pie to sweet-potato-pie

Because I really don't like mixing underscores and dashes in my file
names!
coffee: aeropress: day 3 experiment notes

This concludes the bulk of the coffee storage experiment. Some future
testing on repeated warming and cooling of beans from refridgeration
would be useful.

Signed-off-by: Ezra Savard <git@ezrasavard.com>