Fix go_vet and golint issues

[njourdane]

I made a PR to add Nuklear in the awesome-go list.

It seems that one required thing for this is to fix some issues in the go_vet and golint, as explained by a collaborator:

The goreportcard-tool lists the result of a few common linters used for go projects. Vet for example reports suspicous constructs, whereas golint lists some formal issues.

Most of those issues can be quickly fixed and in addition to improve code quality, figuring in the awesome-go list will improve Nuklear visibility.

[xlab]

Since it's just a lot of bindings, I'm afraid it'd be hard to pass those tests in the code that is generated and optimised for Cgo.

Also, I honestly don't see profit from making Nuklear more visible, it's relative hard to use.
I'd better choose https://github.com/fyne-io/fyne if I'm about to start an GUI project.

Cheers. Thanks for PR, I'll see what I can do.