Bugfix for class attribute without a value

Author: tehaef

foundation_formtags/templates/foundation_formtags/foundation_form_field.html

@@ -15,7 +15,7 @@
     {% endif %}
 
     {% if field.label %}
-        <label for="{{ field.auto_id }}" class={% if field.errors %}"is-invalid-label"{% endif %}>
+            <label for="{{ field.auto_id }}"{% if field.errors %} class="is-invalid-label"{% endif %}>
             {{ field.label|safe }}
             {% if not field.field.required and use_optional %}
                     <span class="optional">(optional)</span>