[conda] Fix recipe by setting caffe dependence to work on "linux" only

2 jobs for conda-linux-only-fix in 4 minutes and 19 seconds (queued for 3 seconds)
Name Stage Failure
build_macosx_36 Build
    reraise(exc_type, exc_value, tb)
File "/Users/gitlab/builds/b6d3167a/0/bob/bob.ip.mtcnn/miniconda/lib/python3.7/site-packages/jinja2/_compat.py", line 37, in reraise
raise value.with_traceback(tb)
File "/Users/gitlab/builds/b6d3167a/0/bob/bob.ip.mtcnn/conda/meta.yaml", line 30, in top-level template code
- setuptools
File "/Users/gitlab/builds/b6d3167a/0/bob/bob.ip.mtcnn/miniconda/lib/python3.7/site-packages/conda_build/jinja_context.py", line 258, in pin_compatible
"Is it one of your host dependencies?".format(package_name))
RuntimeError: Could not get compatibility information for caffe package. Is it one of your host dependencies?
ERROR: Job failed: exit status 1