Suggestion: allow empty attribute value when event modifier is used

[HerringtonDarkholme]

More specifically, only stop and prevent should be allowed.

Tell us about your environment

• ESLint Version: 4.0.0
• eslint-plugin-vue Version: 3.1.3
• Node Version: 8

Please show your full configuration:

Vanilla

What did you do? Please include the actual source code causing the issue.

<template>
<el-from @submit.native.prevent></el-form>
</template>

What did you expect to happen?

No error. Since this is illustrated in the official doc. https://vuejs.org/v2/guide/events.html#Event-Modifiers

What actually happened? Please include the actual, raw output from ESLint.

Error. 'v-on' directives require that attribute value .
vuejs/vetur#279

[KaelWD]

Can the message be updated to be actual english? I still can't understand what it's trying to say.