Feature: Add CC-BY-4.0 license

[sfinkens]

Before You Begin

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• I have checked for similar feature requests in the project's issue tracker
  to avoid duplicates.
• I have searched existing issues to see if this feature has been discussed
  before.

Feature Details

Is your feature request related to a problem? Please describe

licensecheck currently doesn't recognize the CC-BY-4.0 license.

Describe the solution you'd like

CC-BY-4.0 to be added as type License.PUBLIC.

termToLicense = {
	...
	"CC-BY-4.0": L.PUBLIC,
        ...
}

Describe alternatives you've considered

None

Additional Context

None