[fix] make /stats more CSP compliant - github issue form

Hide textarea from github issue form::

    ./__common__/new_issue.html:6:    <textarea name="body" style="display: none;">{{- '' -}}

BTW: fix indentation.

Reported-by: https://github.com/searxng/searxng/issues/57


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>