fix: downstream dts for fp-ts types

[jacob-alford]

fixes a typescript edge case for buildable packages which export dts containing type inferences for fp-ts types

[coveralls]

Pull Request Test Coverage Report for Build 5881492761

• 14 of 14 (100.0%) changed or added relevant lines in 6 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 5778343264:	0.0%
Covered Lines:	2430
Relevant Lines:	2430

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💛 - Coveralls