vendor in hex_core

[starbelly]

In order to provide a consistent experience we should consider vendoring in hex_core. This specifically helps mitigate against stale cases where by a user has upgraded rebar3_hex but for some reason an old version of hex_core is still around and a lot of trouble shooting ensues.

We have had to help people with this very issue quite a few times on erlanger slack, enough to justify vendoring IMO.

[paulo-ferraz-oliveira]

Did you try the new vendor command from rebar3 yet? I'm not sure it's still experimental, but it worked for me™️ the last time I used it.

[ferd]

rebar3 vendoring only is supposed to work for umbrella applications and won't apply to dependencies, which a plugin is.