fixing btn_classes customization

basetheme_bootstrap/templates/basetheme_bootstrap/form_host.html

@@ -33,7 +33,7 @@
         <a role="button" class="btn btn-primary" href="{{cancel_url}}">{{ cancel_text|default:"Cancel"}}</a>
         {%endif%}
         <div class="form-class {{btn_container_classes|default:'pull-right'}}">
-            <button class="btn btn-primary {{btn_classes}}" type="submit">{{ submit_text|default:"OK" }}</button>
+            <button class="{{btn_classes|default:'btn btn-primary'}}" type="submit">{{ submit_text|default:"OK" }}</button>
         </div>
     </form>
 </div>

basetheme_bootstrap/templates/registration/small_form_host.html

@@ -17,7 +17,7 @@
         {%if form%}{{ form|crispy }}{%endif%}
         {%if cancel_url%}<a role="button" class="btn btn-primary" href="{{cancel_url}}">{{ cancel_text|default:"Cancel" }}</a>{%endif%}
         <div class="form-class {{btn_container_classes|default:'pull-right'}}">
-        <button class="btn btn-primary {{btn_classes}}" type="submit">{{ submit_text|default:"OK" }}</button>
+        <button class="{{btn_classes|default:'btn btn-primary'}}" type="submit">{{ submit_text|default:"OK" }}</button>
         </div>
     </form>
 </div>