bump deps

Author: haoxin

package.json

@@ -17,13 +17,13 @@
     "index.js"
   ],
   "devDependencies": {
-    "koa": "^2.0.0-alpha.3",
-    "mocha": "^2.4.5",
-    "supertest": "^1.2.0"
+    "koa": "^2.3.0",
+    "mocha": "^4.0.1",
+    "supertest": "^3.0.0"
   },
   "license": "MIT",
   "dependencies": {
-    "debug": "*",
+    "debug": "^3.1.0",
     "path-to-regexp": "^2.1.0"
   },
   "engines": {