Removed deprecated bootstrap classes

app/views/projects/issues/show.html.haml

@@ -18,7 +18,7 @@
         %span.hidden-sm.hidden-md.hidden-lg
           = icon('circle-o')
 
-    %a.btn.btn-default.pull-right.visible-xs.gutter-toggle.js-sidebar-toggle{ href: "#" }
+    %a.btn.btn-default.pull-right.visible-xs-block.gutter-toggle.js-sidebar-toggle{ href: "#" }
       = icon('angle-double-left')
 
     .issue-meta

app/views/projects/merge_requests/show/_mr_title.html.haml

@@ -4,7 +4,7 @@
       = @merge_request.state_human_name
     %span.hidden-sm.hidden-md.hidden-lg
       = icon(@merge_request.state_icon_name)
-  %a.btn.btn-default.pull-right.visible-xs.gutter-toggle.js-sidebar-toggle{ href: "#" }
+  %a.btn.btn-default.pull-right.visible-xs-block.gutter-toggle.js-sidebar-toggle{ href: "#" }
     = icon('angle-double-left')
   .issue-meta
     %strong.identifier