Support space titles

[yuhongda0315]

https://github.com/superbiger/vuepress-plugin-tabs/blob/8a95a435b5f18ab402fa7969c4a35ce5e50879be/lib/markdownItPlugin.js#L48

I think space titles should be supported，such as:

/* 
  (1)label="title"&lazy
  (2)label="this is title"&lazy
*/
function getTabAttributes(info) {
  return info.split('&').join(' ');
}

Full demo:

:::: tabs

::: tab javascript
``` label="javascript demo"&lazy
() => {
  console.log('Javascript code example')
}
```
:::

::::

😄😄😄

[Kaifuny]

@yuhongda0315 good issure。 Better compatibility with '& nbsp;'

:::: tabs
::: tab javascript code example lazy
:::
::::