Improve the deprecation notice for ipc module

Close #3577.

atom/browser/api/lib/ipc.coffee

@@ -1,6 +1,6 @@
 {deprecate, ipcMain} = require 'electron'
 
 # This module is deprecated, we mirror everything from ipcMain.
-deprecate.warn 'ipc module', 'ipcMain module'
+deprecate.warn 'ipc module', 'require("electron").ipcMain'
 
 module.exports = ipcMain

atom/renderer/api/lib/ipc.coffee

@@ -2,7 +2,7 @@
 {EventEmitter} = require 'events'
 
 # This module is deprecated, we mirror everything from ipcRenderer.
-deprecate.warn 'ipc module', 'ipcRenderer module'
+deprecate.warn 'ipc module', 'require("electron").ipcRenderer'
 
 # Routes events of ipcRenderer.
 ipc = new EventEmitter