Fixed bad field name

templates/_email/users/activation/user_plain.html

@@ -6,5 +6,5 @@
 {{ super() }}
 
 {% trans %}We require our members to prove validity of e-mail address used during registration. To prove that you are owner of e-mail address used to create this account, click the link below:{% endtrans %}
-{{ board_address }}{% url 'activate' username=user.username, user=user.id, token=user.token %}
+{{ board_address }}{% url 'activate' username=user.username_slug, user=user.id, token=user.token %}
 {% endblock %}