chore(typescript 1.6 upgrade): fix build.tools

tools/broccoli/broccoli-writer.d.ts

@@ -1,6 +1,8 @@
 /// <reference path="../typings/es6-promise/es6-promise.d.ts" />
 
-
-declare class Writer { write(readTree: (tree) => Promise<string>, destDir: string): Promise<any>; }
-
-export = Writer;
+declare module "broccoli-writer" {
+  class Writer {
+    write(readTree:(tree) => Promise<string>, destDir:string):Promise<any>;
+  }
+  export = Writer;
+}