Update dependency license-expression to v21

This MR contains the following updates:

Package	Type	Update	Change
license-expression	dependencies	major	^1.2 -> ^21.6

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Release Notes

nexB/license-expression

v21.6.14

Compare Source

Added

- Switch to calver for package versioning to better convey the currency of the
  bundled data.

- Include https://scancode-licensedb.aboutcode.org/ licenses list with
  ScanCode (v21.6.7) and SPDX licenses (v3.13) keys. Add new functions to
  create Licensing using these licenses as LicenseSymbol.

- Add new License.dedup() method to deduplicate and simplify license expressions
  without over simplifying.

- Add new License.validate() method to return a new ExpressionInfo object with
  details on a license expression validation.

Changed

• Drop support for Python 2.
• Adopt the project skeleton from https://github.com/nexB/skeleton and its new configure script

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