during `mix firmware` ERROR: Unexpected executable format

[s3vus]

I can include it in a project but it dies on mix firmware:

MIX_TARGET=rpi2 mix firmware

Nerves environment
  MIX_TARGET:   rpi2
  MIX_ENV:      dev

|nerves_bootstrap| Building OTP Release...

* skipping runtime configuration (config/releases.exs not found)
* creating _build/rpi2_dev/rel/nerves_thermo/releases/0.1.0/vm.args
Updating base firmware image with Erlang release...
scrub-otp-release.sh: ERROR: Unexpected executable format for '/projects/nerves_thermo/_build/_nerves-tmp/rootfs-additions/srv/erlang/lib/nerves_dht-1.1.3/priv/nerves_dht'

Got:
 file:Mach-O 64-bit executable x86_64

Expecting:
 readelf:ARM;0x5000400, Version5 EABI, hard-float ABI

This file was compiled for the host or a different target and probably
will not work.

Check the following:

1. Are you using a path dependency in your mix deps? If so, run
   'mix clean' in that directory to avoid pulling in any of its
   build products.

2. Did you recently upgrade to Nerves 1.3 or Distillery 2.0? Make
   sure that your 'rel/config.exs' has 'plugin Nerves'. See
   https://hexdocs.pm/nerves/updating-projects.html#updating-from-v1-0-to-v1-3-0

3. Did you recently upgrade or change your Nerves system? If so,
   try cleaning and rebuilding this project and its deps.

4. Are you building outside of Nerves' mix integration? If so,
   make sure that you've sourced 'nerves-env.sh'.

If you're still having trouble, please file an issue on Github
at https://github.com/nerves-project/nerves_system_br/issues.

** (Mix) Nerves encountered an error. %IO.Stream{device: :standard_io, line_or_bytes: :line, raw: true}