Fix template syntax error

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/html/mail/new_contributor.html

@@ -9,7 +9,7 @@
 </p>
 
 <p>
-{% blocktrans and user.first_name as username %}{{ username }} has just made a first contribution on {{ translation }} at {{ site_title }}.{% endblocktrans %}
+{% blocktrans with user.first_name as username %}{{ username }} has just made a first contribution on {{ translation }} at {{ site_title }}.{% endblocktrans %}
 <p>
 
 {% include "mail/footer.html" %}

weblate/html/mail/new_contributor.txt

 {% load url from future %}{% load i18n %}{% load translations %}{% autoescape off %}{% filter wordwrap:72 %}{% trans "Hi," %}
 
-{% blocktrans and user.first_name as username %}{{ username }} has just made a first contribution on {{ translation }} at {{ site_title }}.{% endblocktrans %}
+{% blocktrans with user.first_name as username %}{{ username }} has just made a first contribution on {{ translation }} at {{ site_title }}.{% endblocktrans %}
 
 {% endfilter%}{% endautoescape %}{% include "mail/footer.txt" %}