Fix midi_converter plugin instantiation in lv2lint

[cbix]

Can't tell what exactly is missing here, but this does not happen for any other plugin.

$ lv2lint https://github.com/Stazed/rakarrack-plus#midi_converter

<https://github.com/Stazed/rakarrack-plus#midi_converter>
    [FAIL]  Plugin Instantiation
              failed to instantiate
              seeAlso: <http://lv2plug.in/ns/lv2core>
    [FAIL]  Plugin Symbols
              binary exports superfluous globally visible symbols: 
                * _ZN4Ring10setpanningEi
                * _ZN8Resample8mono_outEPfS0_idi
                * _ZN9MuTroMojo9setpresetEi
                * _ZN12AnalogFilter11filterout_sEf
                * _ZN8Sequence7cleanupEv
                * _ZN8VaryBand10initializeEv
                * _ZN5ArpieD0Ev
                * _ZN8Echotron6getparEi
                * _ZN10StereoHarm7cleanupEv
                * _Z10run_voclv2Pvj
                * ... there is more, but the rest is being truncated
              seeAlso: <http://lv2plug.in/ns/lv2core#binary>
    [WARN]  Plugin Project
              lv2:project doap:name not found
              seeAlso: <http://lv2plug.in/ns/lv2core#project>
  {4 : MIDI_IN}
    [FAIL]  Port Atom Port
              atom:AtomPort requires urid:map feature
              seeAlso: <http://lv2plug.in/ns/ext/urid#map>
  {5 : MIDI_OUT}
    [FAIL]  Port Atom Port
              atom:AtomPort requires urid:map feature
              seeAlso: <http://lv2plug.in/ns/ext/urid#map>

[Stazed]

Thank you for tracking this down! Before you sent the PR I found the missing required urid map but did not catch the unnecessary worker requirement. I have made the changes manually in the wip branch. Again thanks, it probably would have taken me forever to notice the worker issue!!!

[cbix]

Alright, I see :) Would it help to open PRs towards your wip branch instead of master for future contributions?

[Stazed]

Yes, that is generally the latest and where most PRs should go to avoid merge issues. Not a big deal though, thanks again.