Improve Vue version detection

[damianstasik]

I installed Vue with yarn add vue@3 and Yarn added "vue": "3" to package.json and then I configured Vetur to lint my code. For some reason I was getting vue/no-multiple-template-root error in a Vue 3 project, I removed Vue and then reinstalled it, but with a specific version and the error was gone. I changed the regexp inside inferVueVersion to handle such cases where only major version is saved in package.json.

[yoyo930021]

Good catch, Thank you.