A custom '=destroy' hook which takes a 'var T' parameter is deprecated

[drkameleon]

Somewhere in our internal GMP wrapper, we keep getting this warning:
    
    
     Warning: A custom '=destroy' hook which takes a 'var T' parameter is 
deprecated; it should take a 'T' parameter [Deprecated]
    
    
    Run

The code triggering it: 
<https://github.com/arturo-lang/arturo/blob/master/src/helpers/bignums.nim#L95>

And the `finalizeInt` implementation: 
<https://github.com/arturo-lang/arturo/blob/master/src/extras/gmp.nim#L801-L802>

Any idea what is going on here exactly and/or how we could solve it?