sample can't be compiled
Hi. I tried to compile sample example_02_controls.nim, but compilation was failed:
```
Hint: unicode [Processing]
/home/r3d9u11/.nimble/pkgs/nigui-0.1.0/nigui.nim(927, 24) Error: invalid character constant
```
NiGUI installed via Nimble, Linux Mint 18.2.
What I'm doing wrong?