class-based argument prepare doesn't support callable objects

[modosc]

in the old api, something like this works:

class MyPreparer
  def call(arg, ctx)
   # ...
   end
end

# then somewhere else
argument :id, !types.ID, "Vehicle Model ID", prepare: MyPreparer.new

but in the class based api it seems that prepare must be a Proc:
https://github.com/rmosolgo/graphql-ruby/blob/master/lib/graphql/schema/argument.rb#L99

would you accept a pr that allows anything that responds to #call here or was this decision intentional?

thanks!

[rmosolgo]

It was accidental! A PR would be great.

[modosc]

ping - any issues with the pr as-is?