Adding support for vim compiled with python3 support

[juanwolf]

Hi,

Great work for this project !
Except that was not working for me because I'm using vim compiled with python3 support not python so the autoload/browserlink.vim script was giving me some errors.

I replaced few elements to make it work but it would be nice if there's a way to manage both.

I did a pull request to show you what I've changed to make it work, if it can help.

Sorry first pull request of my life, so I opened an issue AND a pull request 👎

[jaxbot]

This would break it for anyone who has only python and not python3, though. Ultimately it probably needs a wrapper, like this: https://github.com/jaxbot/github-issues.vim/pull/57/files

As for the first PR, congratulations! And yes, it is fine to have both a PR and an issue, though the issue would typically be phrased as a bug statement ("Does not work with only python3") instead of a fix title. But works either way, I'm not picky :p