RethinkDB 1.15.2

Closes #34115.

Signed-off-by: Tim D. Smith <git@tim-smith.us>
rethinkdb: update 1.15.2 bottle.
Add support for delta and creduce

The delta formula is derived primarily from
https://github.com/rgov/homebrew-etc.
creduce: add 2.2.1 bottle.
delta: add 2006.08.03 bottle.