boost upgrade to 1.69.0
https://github.com/alpinelinux/aports/pull/4657
Other packages are unhappy with 1.67.0:
meson.build:178: WARNING: Your Boost version 1.67 is known to be buggy, and the MPD build will fail. Please upgrade to Boost 1.68 or later.
(from redmine: issue id 10162, created on 2019-03-26, closed on 2019-06-19)