Store vscode version in `package.json` for reproducible builds

package.json

@@ -1,7 +1,8 @@
 {
 	"name": "monaco-editor",
-	"private": true,
 	"version": "0.31.0",
+	"vscode": "7db1a2b88f7557e0a43fec75b6ba7e50b3e9f77e",
+	"private": true,
 	"description": "A browser based code editor",
 	"author": "Microsoft Corporation",
 	"license": "MIT",