Fix tooling for the example

Apparently we do need opn-cli.

package.json

@@ -28,6 +28,7 @@
     "jshint": "^2.5.6",
     "npmpub": "^3.1.0",
     "nyc": "^11.4.1",
+    "opn-cli": "^3.1.0",
     "serve": "^6.4.4",
     "tap-nyc": "^1.0.3",
     "tap-spec": "^4.1.1",
@@ -41,7 +42,7 @@
     "test": "npm run lint && npm run tests | tap-spec",
     "coverage-tests": "npm run tests | tap-nyc",
     "coverage": "nyc -x \"tests/**\" npm run coverage-tests",
-    "example": "serve -o -p 3000 ./example",
+    "example": "opn http://localhost:3000/example/ && serve -p 3000 .",
     "prepublish": "npm run standalone",
     "release": "npmpub"
   }