For a more complete answer: http://www.compulsivecoders.com/tech/vuejs-component-template-should-contain-exactly-one-root-element/
But basically:
To install it:
npm install vue-fragment
To use it:
import Fragment from 'vue-fragment';
Vue.use(Fragment.Plugin);
// or
import { Plugin } from 'vue-fragment';
Vue.use(Plugin);
Then, in your component:
<template>
<fragment>
<tr class="hola">
...
</tr>
<tr class="hello">
...
</tr>
</fragment>
</template>