Enabling flex-grow for placeholders heading.

[CaptainFalcon92]

As an attempted to use vue-content-placeholder inside a Bootstrap 4 .list-group component...

<ul class="list-group">
    <content-placeholders v-for="n in 8" class="list-group-item" :rounded="true">
        <content-placeholders-heading :img="true"/>
    </content-placeholders>
</ul>

...i added flex: 1; to the .vue-content-placeholders-heading rules, allowing it to expand.