Add devDependency "vscode ^1.1.17" to package.json

[houhoulis]

npm install fails without it, on the postinstall script.

[houhoulis]

I would like VSCodium users, including me 😇 , to be able to use your excellent extension. I used it in VSCode, but I have shifted to VSCodium. ("Free/Libre Open Source Software Binaries of VS Code".)

I should explain a bit more about the options for publishing your extension to be used in VSCodium. The "Open VSX Registry" (https://open-vsx.org) is a registry of open-source VS Code extensions. Any development environment can access extensions there. The Microsoft Marketplace is not open to outside access.

Since npm install is failing right now on master, this extension can't be built, so it's not in shape for submission. But if the build were succeeding, your extension could be published or added to the OpenVSX registry. Hence this PR.

Once the build is succeeding, you could publish your extension officially to the OpenVSX Registry as the maintainer. Alternatively, I (or anyone) could add the extension to the registry without publishing it. You'd be the author in both cases. The extension would appear in VSCodium exactly the same as it does in VSCode, in both cases.

Here's their quote about these two methods of adding an extension:

One goal of Open VSX is to have extension maintainers publish their extensions according to the documentation. However, you may be missing specific extensions that have not been published by their maintainers: either they are not willing to do it, or they haven't found time to do it, or simply they haven't heard about Open VSX yet. Though the preferred solution for such a situation is to convince the maintainers to start publishing themselves, you can add the extensions here [ https://github.com/open-vsx/publish-extensions#how-to-add-an-extension ] to have them published by our CI workflow.

If you are amenable to making this available for VSCodium users, please merge this PR (hopefully it fixes the build?) and let me know whether you'd like to publish it officially to the registry as the maintainer. If you'd rather not bother, I can submit it via their CI.

Thank you.