Upgrade Vue to >=2.2.0 and disable development warnings in tests

Right now the js-spec output is riddled with Vue.js warnings:

You are running Vue in development mode.
Make sure to turn on production mode when deploying for production.
See more tips at https://vuejs.org/guide/deployment.html

As of version 2.2.0 vue has a setting Vue.config.productionTip which can be set to false to disable this output.

Some more info can be found here: https://github.com/vuejs/vue/pull/4907

// @psimyn