removes gofork direct usage as fix is part of go
fixes https://github.com/Shopify/sarama/issues/1438
`jcmturner/gokrb5` needs to use the `jcmturner/gofork` in order to have
some workarounds about some stuff not implemented or not working as
expected.
For the specific case of github.com/jcmturner/gofork/encoding/asn1 there
is no reason right now to keep using `jcmturner/gofork` as the issue
golang/go#17321 was solved/closed in Dec 15, 2016 and released in go
1.10
`jcmturner/gokrb5` still uses internally `jcmturner/gofork`, it seems
the `gofork` `asn1` part could be removed and use the standar library,
but that will need some more work and PRs on the `jcmturner/gokrb5`
side.
Diego Alvarez