go.mod, go.sum: Update goleveldb

[kcalvinalvin]

Goleveldb recently had a PR in where memory allocation was reduced
drastically (github.com/syndtr/goleveldb/pull/367). Update goleveldb
to use that PR.

[coveralls]

Pull Request Test Coverage Report for Build 1200463786

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 7 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.03%) to 52.912%

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Files with Coverage Reduction	New Missed Lines	%
mempool/mempool.go	1	66.75%
peer/peer.go	2	75.71%
database/ffldb/blockio.go	4	92.62%

Totals
Change from base Build 1193116021:	0.03%
Covered Lines:	21023
Relevant Lines:	39732

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💛 - Coveralls

[jcvernaleo]

@kcalvinalvin could you rebase this? Looks like a good one to get in but need the right tests to run and need that one conflict fixed.