Generate .tern-project with vue init

[Yamakaky]

Following of vuejs/vue-cli#404.

[LinusBorg]

I'm not too convinced that we should add another config file to the template people have to know about ("what is this for? should I do something with it?"), especially when it's about something like ternjs (which is a great project, but ...) which is not required to use this template's functionality and olny used by a fraction of developers.