Move -font parameter before label parameter

[SuperTux88]

I just had the problem from #52, but the fix from #55 didn't help, still the same error message.

After a bit of try and error I found out, that the order of the parameters matter and the -font parameter needs to be before the label:. So this fails:

convert label:foo -font DejaVu-Sans jpeg:-

while this works:

convert -font DejaVu-Sans label:foo jpeg:-

(tested on debian stretch)

[SuperTux88]

Oh, I just found #57 ... so I close this again. But can you please merge and release #57 then? :)