Update to 6.0.0

[Tomas-M]

This address is yours?
https://zcash.github.io/rpc/

If so, Zcash is version 6.0.0 already, please update your documentation
If you search google for "zcash rpc documentation", your site is first result,
it even seems like docs for 6.0.0 but in fact it is 5.10 { https://zcash.github.io/rpc/ }
Thank you