Update project metadata to use SPDX license identifier

[cdce8p]

Proposed change

The official (SPDX) short identifier for the Apache License 2.0 is Apache-2.0.
https://spdx.org/licenses/Apache-2.0.html

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (which adds functionality to this library)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:

Checklist

• The code change is tested and works locally.
• Tests have been added to verify that the new code works.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (ef3db68) to head (3ca8215).
Report is 22 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #653   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           17        17           
  Lines         1428      1425    -3     
=========================================
- Hits          1428      1425    -3     

Flag	Coverage Δ
3.10	100.00% <ø> (ø)
3.11	100.00% <ø> (ø)
3.12	100.00% <ø> (ø)
3.8	100.00% <ø> (ø)
3.9	100.00% <ø> (ø)

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[gerard33]

Thx.