doesn't seem to respect build_dir setting

[gwhitney]

To reproduce, copy/edit the examples/ok-mkdocs-docs-merge example so that the mkdocs-test.yml file looks like:

# This example shows how to merge a docs folder with other documentation.
site_name: ok-mkdocs-docs-merge
plugins:
  - simple:
      build_dir: buildit

then run mkdocs build --config-file mkdocs-test.yml. The first line of the output is

INFO    -  mkdocs-simple-plugin: build_dir: /tmp/mkdocs_simple_8onf2elf

but I would expect it to be [...]/ok-mkdocs-docs-merge/buildit. (Just tried this with mkdocs-simple-plugin v3.2.0.)

[athackst]

Thanks for the detailed report, I'll look into it