Correct comments in singature.go

[jcvernaleo]

Fix the typo correction from #2065

[coveralls]

Pull Request Test Coverage Report for Build 7035582109

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 56.047%

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Files with Coverage Reduction	New Missed Lines	%
btcutil/gcs/gcs.go	1	81.25%
peer/peer.go	5	73.49%

Totals
Change from base Build 7034232494:	-0.01%
Covered Lines:	27939
Relevant Lines:	49849

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💛 - Coveralls

[guggero]

Thanks! LGTM 🎉