fix readthedocs updating

[dave-doty]

readthedocs is having errors even though I can compile with Sphinx locally: https://readthedocs.org/projects/scadnano-python-package/builds/22907418/

[rayzhuca]

I think this is due to the new changes that buildthedocs rolled out:
https://blog.readthedocs.com/use-build-os-config/
I'll create a new branch that adds the new configs in readthedocs.yml.

[dave-doty]

Here's the latest error (after fixing the build.os issue in PR #292): https://readthedocs.org/projects/scadnano-python-package/builds/22917882/

[rayzhuca]

Merged #296 and dev built successfully https://readthedocs.org/projects/scadnano-python-package/builds/23148921/.

[dave-doty]

In general we only close issues when they make it to the main branch (that's the main reason to have main be the default branch, so that commit messages with phrases such as "closes #<issue_number>" will automatically close them, but only when that commit makes it to the main branch), but maybe because this involves readthedocs it is already fixed? Essentially let's leave this open until we've fixed the issue totally (i.e., the readthedocs site shows the correct documentation), but I haven't checked to see if it's really fixed yet.