upgrade tunnel-proxy to 0.4.0

  to avoid node 0.11.x issue (request#779)

package.json

@@ -31,7 +31,7 @@
   "optionalDependencies": {
     "tough-cookie": ">=0.12.0",
     "form-data": "~0.1.0",
-    "tunnel-agent": "~0.3.0",
+    "tunnel-agent": "~0.4.0",
     "http-signature": "~0.10.0",
     "oauth-sign": "~0.3.0",
     "hawk": "~1.0.0",