fix build on Plan 9

[fhs]

Fixes #7575
Fixes #7671

ipfs/go-ds-badger#100 should be merged before this PR. I'm using an indirect dependency as a workaround. (done)

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[willscott]

the badger dep update merged to master, do you need a release of go-ds-badger for this to refer to?

[fhs]

the badger dep update merged to master, do you need a release of go-ds-badger for this to refer to?

@willscott Yes, I need a new release of go-ds-badger. Thanks.

[willscott]

https://github.com/ipfs/go-ds-badger/releases/tag/v0.2.5

[fhs]

I've updated go-ds-badger to the new version. This PR is ready for review.

[willscott]

Looks good to me. @aschmahmann for second review / merge

[aschmahmann]

Looks good, thanks 😄. Just added a question about a dependency change.

Also, it looks like the sharness tests are failing (perhaps due to the dependency change).