fix invalid error log message

[foosinn]

a run of go test ./... failed for me due to an invalid Errorf statement.

[k3a]

You should probably use %v to make it consistent with other errors in the repo.
There doesn't seem to be difference now (https://play.golang.org/p/01OEs7caVsA) but I think there used to be difference in previous Go versions.

[foosinn]

Updated to use %v

[mhrabovcin]

@jr0d can we merge this one?

[jr0d]

Thanks @foosinn