message: refactor: fix template lint in error-page
diff: -{{title (t (concat translateKey '.heading'))}}
  +{{title (t (concat this.translationKey '.heading'))}}
  -<div class="container">
  - <div class="row">
  - <div class="col-xs-12">
  - <h1>{{t (concat translateKey '.heading')}}</h1>
  +<div class='container'>
  + <div class='row'>
  + <div class='col-xs-12'>
  + <h1>{{t (concat this.translationKey '.heading')}}</h1>
  <p>
  - {{t (concat translateKey '.message')}}
  + {{t (concat this.translationKey '.message')}}
  <br>
  <span>
  {{t 'app_components.error_page.email_message'}}
  <a
  - href="mailto:{{supportEmail}}"
  - onclick={{action 'click' 'link' (concat label ' - Support') target=analytics}}
  + href='mailto:{{this.supportEmail}}'
  + onclick={{action 'click' 'link' (concat this.label ' - Support') target=this.analytics}}
  >
  - {{supportEmail}}
  + {{this.supportEmail}}
  </a>
  </span>
  </p>
  - {{#if theme.isProvider}}
  + {{#if this.theme.isProvider}}
  <a
  - class="btn btn-primary m-t-md"
  - href={{theme.pathPrefix}}
  - onclick={{action 'click' 'link' (concat label ' - Go to Index') target=analytics}}
  + class='btn btn-primary m-t-md'
  + href={{this.theme.pathPrefix}}
  + onclick={{action 'click' 'link' (concat this.label ' - Go to Index') target=this.analytics}}
  >
  {{t 'app_components.error_page.go_to'
  - brand=(t @brandKey name=theme.provider.name)
  + brand=(t @brandKey name=this.theme.provider.name)
  }}
  </a>
  {{else}}
  - {{#link-to-external 'home' class="btn btn-primary m-t-md"}}
  + {{#link-to-external 'home' class='btn btn-primary m-t-md'}}
  {{t 'app_components.error_page.go_to' brand=(t 'general.OSF')}}
  {{/link-to-external}}
  {{/if}}
  