add missing @ to the onboarding modal (#4560)

app/javascript/mastodon/features/ui/components/onboarding_modal.js

@@ -30,7 +30,7 @@ const PageOne = ({ acct, domain }) => (
     <div>
       <h1><FormattedMessage id='onboarding.page_one.welcome' defaultMessage='Welcome to Mastodon!' /></h1>
       <p><FormattedMessage id='onboarding.page_one.federation' defaultMessage='Mastodon is a network of independent servers joining up to make one larger social network. We call these servers instances.' /></p>
-      <p><FormattedMessage id='onboarding.page_one.handle' defaultMessage='You are on {domain}, so your full handle is {handle}' values={{ domain, handle: <strong>{acct}@{domain}</strong> }} /></p>
+      <p><FormattedMessage id='onboarding.page_one.handle' defaultMessage='You are on {domain}, so your full handle is {handle}' values={{ domain, handle: <strong>@{acct}@{domain}</strong> }} /></p>
     </div>
   </div>
 );