Incompatible units error

[Crustan]

Hi!

Im using mappy-breakpoints (v. 0.2.3) like this:

$breakpoints: (
  's' : 36em,
  'm' : 48em, 
  'l' : 64em,  
);

@include mappy-bp(s m){
  //Doing some styles
};

But I get this error:

sass\1-vendor\_mappy-breakpoints.scss
Error: Incompatible units: 'px' and 'em'.
        on line 129 of sass/1-vendor/_mappy-breakpoints.scss
>>     $_maxw: mappy-convert-to-em($_maxw - 1px);

EDIT:
Got it to work after changing
$_maxw: mappy-convert-to-em($_maxw - 1px);
to
$_maxw: mappy-convert-to-em($_maxw - mappy-em(1px));

[zellwk]

Interesting error. Let me get to it when I find some time on my hands.

[X-Y]

Encountered the issue again, I made a PR to allow more general units:

#28