Update for Vue 2.0

[ryanhightower]

• Updated directive to more closely match the original using Vue 2.0
• Updated karma.conf to properly use new Vue standalone compiler in tests
• Updated tests to pass.

[bradlis7]

Worked for me. I'm not sure the difference between this and #17 though, but I saw this one first. I think the original project may be abandoned.

[codewp]

@sagalbot Please let us know why you did not merge any of PRs which are related to vue2 support?

[codewp]

Installing it via npm package.json

"dependencies": {
    "vue-sortable": "https://github.com/ryanhightower/vue-sortable#661cf284a6a531a45d4ad92fd592dce0301a3dba"
  },

after adding it to dependencies run npm install.