helptext: fix a recent typo
Differential Revision: https://phab.mercurial-scm.org/D10033
{header}
<!-- Changelog -->
<id>{urlbase}{url|urlescape}</id>
<link rel="self" href="{urlbase}{url|urlescape}atom-log"/>
<link rel="alternate" href="{urlbase}{url|urlescape}"/>
<title>{repo|escape} Changelog</title>
{latestentry%feedupdated}
{entries%changelogentry}
</feed>