try to fix travis commitizen

It worked on Travis with this configuration before, even though it DOESN'T work locally like this

package.json

@@ -67,7 +67,7 @@
   },
   "config": {
     "commitizen": {
-      "path": "cz-conventional-changelog"
+      "path": "./node_modules/cz-conventional-changelog"
     }
   }
 }