Bump requests from 2.18.4 to 2.20.0

Bumps [requests](https://github.com/requests/requests) from 2.18.4 to 2.20.0.
- [Release notes](https://github.com/requests/requests/releases)
- [Changelog](https://github.com/psf/requests/blob/master/HISTORY.md)
- [Commits](https://github.com/requests/requests/compare/v2.18.4...v2.20.0)

Signed-off-by: dependabot[bot] <support@github.com>

Harvest requires either a link to the application or an email address to
be included in the 'User-Agent' header with requests to their API
(https://help.getharvest.com/api-v2/introduction/overview/general/#api-requests).

GitHub's parser didn't like my indentation, which was held over from
before the Markdown conversion.

* The code blocks don't need to be double-indented.
* Change the list indentation so that the bullets appear at the start of
  the text of the previous bullet. Otherwise GitHub turns them into
  blockquotes.

Markdown apparently doesn't support letter lists (what?), so use a
markup language that actually does.

Give some background, along with installation instructions and license
information.

Otherwise it gets created in the current directory, and this fails when
run from Launchd because that runs at the root of the filesystem.

This will run the program every Monday and Friday evening.

The plist needs to be modified to work in your environment and with your
configuration.