chore: Upgrade vue-i18n to v8.0.0

BREAKING CHANGE: - https://github.com/kazupon/vue-i18n/blob/dev/CHANGELOG.md#800-2018-06-23

Author: paulgv

package.json

@@ -46,7 +46,7 @@
     "esm": "3.0.28",
     "fs": "^0.0.1-security",
     "js-cookie": "^2.2.0",
-    "vue-i18n": "^7.8.0",
+    "vue-i18n": "^8.0.0",
     "vue-i18n-extensions": "^0.1.0"
   },
   "devDependencies": {

yarn.lock

@@ -9919,9 +9919,9 @@ vue-i18n-extensions@^0.1.0:
   dependencies:
     vm2 "^3.5.0"
 
-vue-i18n@^7.8.0:
-  version "7.8.0"
-  resolved "https://registry.yarnpkg.com/vue-i18n/-/vue-i18n-7.8.0.tgz#fa49c3f90d20edab2048e9ef825774d39f1906d9"
+vue-i18n@^8.0.0:
+  version "8.0.0"
+  resolved "https://registry.yarnpkg.com/vue-i18n/-/vue-i18n-8.0.0.tgz#ae0c6e05ec8e36151bcf5f47c7b538c8af6d0282"
 
 vue-loader@^15.2.4, vue-loader@^15.2.6:
   version "15.3.0"