feat(source): added source from constant plugin

[coveralls]

Pull Request Test Coverage Report for Build 701

• 9 of 9 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 696:	0.0%
Covered Lines:	584
Relevant Lines:	584

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💛 - Coveralls

[thebruce]

:tada: This PR is included in version 6.1.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: