Fix the "Paid plan required" notice.

templates/integrations/add_call.html

@@ -13,7 +13,7 @@
         a text-to-speech engine will read out a message and then hang up.
     </p>
 
-    {% if show_pricing and profile.sms_limit == 0 %}
+    {% if show_pricing and profile.call_limit == 0 %}
     <p class="alert alert-info">
         <strong>Paid plan required.</strong>
         Phone call notifications are not available on the free plan–they