Add an option to disable this plugin on non-NixOS system

[lxl66566]

I use vscode and share my vscode extension & settings on multiple platform, including Windows, ArchLinux and NixOS.
On NixOS it works well, but when I open vscode on other OS, I would disturbed by:

Because the extensions and user settings are synced between devices, I cannot just set "nix.enableLanguageServer": false or disable this extension; and I don't want to add this setting item to all of my projects .vscode/settings.json manually.

If there's an option to disable this plugin on non-NixOS system, or some other solutions, I would really appreciate it.

[IronGreninja]

I noticed that there is onStartupFinished activation event when it should be onLanguage:nix, so it will start every time and complain.

[jnoortheen]

@IronGreninja it would no longer be that case #424 .

[IronGreninja]

@jnoortheen That's great. When will it be released?

[jnoortheen]

I will cut a release shortly.

[jnoortheen]

Closing as the PR is now merged.