What type of a PR is this?

• Changes to Existing Features
• New Feature Submissions
• Bug Fix
• Breaking Change (include change in API behaviours, etc.)

Closes frappe/easy_install#16

Please provide enough information so that others can review your pull request:

This fix adds Linux Mint 19 and 20 to the list of supported dists, to allow the installation script to proceed on Linux Mint versions.

Explain the details for making this change. What existing problem does the pull request solve? The following checklist could help

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you lint your code locally prior to submission?
• Have you successfully run tests with your changes locally?
• Does your commit message have an explanation for your changes and why you'd like us to include them?
• Docs have been added / updated
• Tests for the changes have been added (for bug fixes / features)
• Did you modify the existing test cases? If yes, why?

Linux Mint users need to be able to install and setup bench on their machines.

Screenshots/GIFs