Key path should parse if sub path contain spaces

[exoego]

Note

This is basically duplicate a of #502.
I think it should be fixed so I opened a new issue.

vue & vue-i18n version

vue: 2.5.17
vue-i18n: 8.9.0

Reproduction Link

http://jsfiddle.net/vshjg5bq/

Steps to reproduce

<div>{{ $t('PopupMenu.Play Now') }}</div>
<div>{{ $t('Hello World') }}</div>

new VueI18n({
  locale: 'en',
  messages: {
    en: {
      'PopupMenu': {
        'Play Now': 'Play Now'
      },
      'Hello World':'Hello World'
    }
  }
})

What is Expected?

Play Now
Hello World

What is actually happening?

PopupMenu.Play Now
Hello World

Cannot translate the value of keypath 'PopupMenu.Play Now'. Use the value of keypath as default.