Broken plugin link and variant link

https://hub.meltano.com/ -> plugins -> https://meltano.com/docs/plugins.html (301's to docs.meltano.com) https://hub.meltano.com/taps/3plcentral -> variants -> https://docs.meltano.com/#variants etc

There's at least a few more of these on the hub. I think a grep of this repo for all https://meltano.com/docs links would do the trick to get the list