chore(example): use npm pack for relative filepath installation

due to the changes of `"file:"` handling in npm5.
refs: npm/npm#15900 (comment)

.gitignore

@@ -28,4 +28,5 @@ build/Release
 # https://www.npmjs.org/doc/misc/npm-faq.html#should-i-check-my-node_modules-folder-into-git-
 node_modules
 
-
+# ignore tarballs generated by npm pack
+*.tgz

example/package.json

@@ -4,6 +4,7 @@
   "description": "",
   "main": "index.js",
   "scripts": {
+    "postinstall": "npm pack .. | xargs npm install --no-save",
     "test": "mocha",
     "travis-test": "npm i && mocha test/pass-test.js"
   },
@@ -14,7 +15,6 @@
   "license": "MIT",
   "devDependencies": {
     "espower-loader": "^1.0.0",
-    "intelli-espower-loader": "file:..",
     "mocha": "^3.0.0",
     "power-assert": "^1.0.0"
   }