Fixed mobile changelog link

Author: zhukov

app/partials/mobile/changelog_modal.html

@@ -24,7 +24,7 @@ <h3 class="modal_section_header changelog_version_title">
         </h3>
         <div class="modal_section_body changelog_version_changes">
           <ul class="list-unstyled changelog_version_changes_list">
-            <li>Usernames support: <a href="" ng-click="changeUsername">Choose a username right now!</a></li>
+            <li>Usernames support: <a href="" ng-click="changeUsername()">Choose a username right now!</a></li>
             <li>Search can now find public users by username.</li>
             <li>Most popular emoticons shown in 'recent' when empty</li>
             <li>Bugfixes</li>