Ignore files inside `.vscode-test` (#3256)

* Ignore files inside `.vscode-test` 

[vscode-test](https://github.com/microsoft/vscode-test) is a testing framework for vscode extensions. Inside the `vscode-test` folder are stored one or more versions of vscode, which are used for testing a vscode extension.

* Update Node.gitignore

Node.gitignore

@@ -102,3 +102,6 @@ dist
 
 # TernJS port file
 .tern-port
+
+# Stores VSCode versions used for testing VSCode extensions
+.vscode-test