Bumping Vue+VueRouter versions, some minor fixes

Things we fixed

• Revert Change to dev-client.js that broke hot reloading in older browsers
• dev-server.js: Fix a const that should be a let @schettino72 (#965)

Things we improved

• Converted Hello-World compüonent in App.vue to PascalCase to match the new style guide. @hootlex (#951)
• bumped Versions for Vue (2.5.2) and Vue-Router (3.0.1) @Ffloriel (#984)