Please include arvgcstringnode.h in arv.h

I am now trying to write an aravis wrapper in Swift for macOS. I am not sure when, but the umbrella header ‘arv.h’ was missing the header ‘arvgcstringnode.h’. This is not a major problem, but it can be confusing for developers. So please fix it. Thanks.

Hi,

Fixed in main.

Thanks,

Emmanuel.