Drop dependency on subpackage

[mattheworiordan]

See #123 for background.

This from @xshyne88:

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@QuintinWillison

I think this needs to be reopened though I think the OP did not mention that this error happens when you have other dependencies such as https://github.com/spf13/viper. (Also seems etcd, and gin-gonic would also be in conflict).

Here is a link to the codec packages solution.
ugorji/go#299

DataDog forked viper and made this exact change in a commit, here is what they did:
DataDog/viper@2922e44

Thanks for taking a look.