truncate string filter for Vue.js

Vue.js String truncate filter.js

Vue.filter('fm-truncate', function (value, length) {
  if (!value) return ''
  value = value.toString()
  if(value.length > length){
    return value.substring(0, length) + "..."
  }else{
    return value
  }
})


## Example
```
   {{topic.title | fm-truncate(5) }}
```

fm- preview just mean facial mask
you can change the fm-truncate to whatever you like

Vue doc about filter:
https://vuejs.org/v2/guide/filters.html