fix: if header sent, don't set the cookie

bigpipe will fail

package.json

@@ -7,11 +7,10 @@
     "index.js"
   ],
   "scripts": {
-    "test": "eslint . && mocha --harmony --check-leaks -R spec -t 5000 test/*.test.js",
-    "test-cov": "node --harmony node_modules/.bin/istanbul cover node_modules/.bin/_mocha -- --check-leaks -t 5000 test/*.test.js",
+    "test": "eslint . && mocha --check-leaks -R spec -t 5000 test/*.test.js",
+    "test-cov": "istanbul cover _mocha -- --check-leaks -t 5000 test/*.test.js",
     "lint": "eslint .",
     "autod": "autod -w --prefix '~'",
-    "cnpm": "npm install --registry=https://registry.npm.taobao.org",
     "contributors": "contributors -f plain -o AUTHORS"
   },
   "dependencies": {
@@ -25,8 +24,8 @@
     "beautify-benchmark": "0",
     "benchmark": "1",
     "contributors": "*",
-    "eslint": "~1.5.0",
-    "istanbul-harmony": "*",
+    "eslint": "1",
+    "istanbul": "*",
     "koa": "1",
     "mm": "1",
     "mocha": "*",