support rebar2

[andreineculau]

In an attempt to upgrade hackney, I have discovered that I cannot use rebar 2 anymore.
The issue is similar to benoitc/hackney#509, just that it is not idna anymore, but certifi as mentioned also in benoitc/hackney#509 (comment) (after the issue has been closed).

Thus a similar fix is needed here for parse_trans as in idna benoitc/erlang-idna@f01533f

[benoitc]

which error do you have ?

[andreineculau]

Same as in the comment benoitc/hackney#509 (comment)

Dependency not available: parse_trans-3.2.0 (undefined)

[fenollp]

@andreineculau Is there no way to make you move to rebar3?

[andreineculau]

It is not just me the individual but all users of hackney (which @benoitc has said in a commit/issue that has to work with rebar2) and all users of my tool https://github.com/for-GET/katt

So all in all, no.
I know it's not a convenient situation, stemming from rebar3's backward-incompat, but if certifi is not to support rebar2, and then hackney neither, then 1. Would be good to state that in clear and 2. That there was a major semver bump when the incompat switch happens/ed

[benoitc]

it will need another rebar.config.script. i will take care on it.