[node] Export Buffer and SlowBuffer from "buffer" module.

node/node.d.ts

@@ -411,6 +411,9 @@ interface NodeBuffer {
 ************************************************/
 declare module "buffer" {
     export var INSPECT_MAX_BYTES: number;
+    var BuffType: typeof Buffer;
+    var SlowBuffType: typeof SlowBuffer;
+    export { BuffType as Buffer, SlowBuffType as SlowBuffer };
 }
 
 declare module "querystring" {