Fix bug when using delimited-like path.

[ota-meshi]

fixes #245, fixes #260

[andruhon]

I think this change brings false positive on nested messages from json.

Considering the json file, like en-NZ.json

{
 "announcements": {
  "test": "My Test Message"
 }
}

and the function $t('announcements.test') will cause 'announcements.test' does not exist in localization message resources(@intlify/vue-i18n/no-missing-keys)

The 1.0.1 https://github.com/intlify/eslint-plugin-vue-i18n/releases/tag/v1.0.1 does not have such false positive.