fix toggle subscription link for groups

app/assets/javascripts/subscription.js

@@ -19,7 +19,7 @@ class Subscription {
     button.classList.add('disabled');
 
     const isSubscribed = buttonSpan.innerHTML.trim().toLowerCase() !== 'subscribe';
-    const toggleActionUrl = this.containerElm.dataset.url;
+    const toggleActionUrl = this.containerElm.dataset.url.replace(':project_path', gl.issueBoards.BoardsStore.detail.issue.project.path);
 
     $.post(toggleActionUrl, () => {
       button.classList.remove('disabled');

app/views/shared/boards/components/sidebar/_notifications.html.haml

 - if current_user
-  .block.light.subscription{ ":data-url" => "'#{milestones_label_path}/' + issue.iid + '/toggle_subscription'" }
+  .block.light.subscription{ ":data-url" => "'#{build_issue_link_base}/' + issue.iid + '/toggle_subscription'" }
     %span.issuable-header-text.hide-collapsed.pull-left
       Notifications
     %button.btn.btn-default.pull-right.js-subscribe-button.issuable-subscribe-button.hide-collapsed{ type: "button" }