Specify lockfile update for contribution

Author: chenglou

CONTRIBUTING.md

@@ -145,7 +145,7 @@ In the future, we should consier showing the format errors when `.compiler.log`
 
 Currently the release is vetted and done by @chenglou.
 
-- Bump the version properly in `package.json` and make a new commit.
+- Bump the version properly in `package.json` and lockfile and make a new commit.
 - Make sure @ryyppy is aware of your changes. He needs to sync them over to the vim plugin.
 - Use `vsce publish` to publish. Official VSCode guide [here](https://code.visualstudio.com/api/working-with-extensions/publishing-extension). Only @chenglou has the publishing rights right now.
 - Not done! Make a new manual release [here](https://github.com/rescript-lang/rescript-vscode/releases); use `vsce package` to package up a standalone `.vsix` plugin and attach it onto that new release. This is for folks who don't use the VSCode marketplace.