When building the docs with the make html command, if you already have a convert module somewhere else, you can get an error:

File "/Users/sosborne/miniconda3/envs/astroconda/lib/python3.6/subprocess.py", line 438, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['convert', '--version']' returned non-zero exit status 1.

This should probably be fixed by checking if the convert module matplotlib is looking for is actually the correct module, and finding a work around if convert is from another package