support jsdelivr npm cdn like vue package does

[magicdawn]

see difference here:

• https://cdn.jsdelivr.net/npm/vue/package.json
• https://cdn.jsdelivr.net/npm/vuex/package.json

[magicdawn]

why jsdelivr:

With my network conditions (China mainland beijing)

• https://unpkg.com/vue@2.5.22/dist/vue.js cost about 300ms
• https://cdn.jsdelivr.net/npm/vue@2.5.22/dist/vue.js cost about 90~100 ms
  So I choose jsdelivr

[ktsn]

Thank you!