vue: Update eslint-plugin-vue to 7.4.1

[edg2s]

No description provided.

[edg2s]

Current failures:

/var/www/eslint-config-wikimedia/test/fixtures/vue-common/invalid.vue
  11:14  warning  Expected '#name' instead of 'v-slot:name'                                                     vue/v-slot-style
  15:14  warning  Expected '#name' instead of 'v-slot:name'                                                     vue/v-slot-style
  15:14  error    An element cannot have multiple '<template>' elements which are distributed to the same slot  vue/valid-v-slot
  34:2   warning  Unused eslint-disable directive (no problems were reported from 'vue/name-property-casing')
  35:8   warning  Property name "div" is not PascalCase                                                         vue/component-definition-name-casing

✖ 5 problems (1 error, 4 warnings)
  0 errors and 3 warnings potentially fixable with the `--fix` option.

cc @catrope

[jdforrester]

(Waiting for final "go" from Roan.)

[jdforrester]

Also, once this lands, we'll cut a new release, I think; see #340.