"could not load: libgtk-x11-3.0.dylib" on macOS
Calc seemed to build ok on Mac, but couldn't run because of a missing libgtk library. Is there any solution for this?

```
Hint:  [Link]
Hint: operation successful (44662 lines compiled; 4.632 sec total; 72.336MiB peakmem; Debug Build) [SuccessX]
Hint: /Users/Andy/Devel/nim_demos/NiCalc/src/NiCalc  [Exec]
could not load: libgtk-x11-3.0.dylib
compile with -d:nimDebugDlOpen for more information
Error: execution of an external program failed: '/Users/Andy/Devel/nim_demos/NiCalc/src/NiCalc '
```
