api tests should require vscode.d.ts from source

extensions/vscode-api-tests/src/index.ts

@@ -3,6 +3,8 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
+/// <reference path="../../../src/vs/vscode.d.ts" />
+
 //
 // PLEASE DO NOT MODIFY / DELETE UNLESS YOU KNOW WHAT YOU ARE DOING
 //
@@ -25,4 +27,4 @@ testRunner.configure({
 	timeout: 10000
 });
 
-export = testRunner;
\ No newline at end of file
+export = testRunner;