fix typo

src/vs/vscode.d.ts

@@ -128,7 +128,7 @@ declare module 'vscode' {
 		readonly isDirty: boolean;
 
 		/**
-		 * `true` if the document have been closed. A closed document isn't synchronized anymore
+		 * `true` if the document has been closed. A closed document isn't synchronized anymore
 		 * and won't be re-used when the same resource is opened again.
 		 */
 		readonly isClosed: boolean;