v3.21.0

Added:

• All conda packages will have the license file included alongside
  the rendered recipe.
• conda-smithy now reports lint if pin_compatible or pin_subpackage are used
  with the wrong package type.

Changed:

• build_locally now creates conda's shared package cache outside the container,
  so repeated builds of the same recipe do not need to redownload packages.
• mamba is now used in the CI tests for conda-smithy

Fixed:

• Fix the support of idle_timeout_minutes for Travis CI

Authors:

• Isuru Fernando
• Matthew R. Becker
• Leo Fang
• Tim Snyder
• Daniel Ching
• Nicholas Bollweg