feat(package.json): make the repository commitizen-friendly

As discussed with @thetutlage we are going to follow a convention about commit message.

Author: RomainLanz

package.json

@@ -22,6 +22,7 @@
     "co-mocha": "^1.1.2",
     "co-supertest": "0.0.10",
     "coveralls": "^2.11.4",
+    "cz-conventional-changelog": "^1.1.5",
     "formidable": "^1.0.17",
     "istanbul": "^0.4.0",
     "mocha": "^2.3.3",
@@ -52,6 +53,11 @@
     "path-to-regexp": "^1.2.1",
     "type-of-is": "^3.4.0"
   },
+  "config": {
+    "commitizen": {
+      "path": "./node_modules/cz-conventional-changelog"
+    }
+  },
   "directories": {
     "test": "test"
   },