fix(plugin-vuetify): declare vue as a peer dependency

[merceyz]

What's the problem this PR addresses?

vue-cli-plugin-vuetify attempts to require vue but doesn't declare it as a dependency.

vue-cli-plugins/packages/vue-cli-plugin-vuetify/index.js

Line 15 in 4a09f6e

const isVue3 = semver.major(require('vue/package.json').version) === 3

How did you fix it?

Added vue as a peer dependency.