Include typings in addons as well

src/addons/attach/attach.ts

@@ -5,8 +5,6 @@
  * Implements the attach method, that attaches the terminal to a WebSocket stream.
  */
 
-/// <reference path="../../../typings/xterm.d.ts"/>
-
 import { Terminal } from 'xterm';
 import { IAttachAddonTerminal } from './Interfaces';
 

src/addons/attach/tsconfig.json

@@ -7,5 +7,9 @@
     "sourceMap": true,
     "removeComments": true,
     "declaration": true
-  }
+  },
+  "include": [
+    "**/*.ts",
+    "../../../typings/xterm.d.ts"
+  ]
 }