btcd: Change GC percent to 30

[kcalvinalvin]

GC percent was previously set at 10 percent. This repo has had many
PRs that reduced memory allocation. It's now ok to increase the GC
percentage and not use too much system memory.

[coveralls]

Pull Request Test Coverage Report for Build 1438095120

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage remained the same at 54.153%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcd.go	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
peer/peer.go	2	74.82%

Totals
Change from base Build 1435359435:	0.0%
Covered Lines:	25583
Relevant Lines:	47242

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💛 - Coveralls