Removes class 'btn-link' of Revoke button

CHANGELOG

@@ -6,6 +6,7 @@ v 8.13.0 (unreleased)
 v 8.12.2 (unreleased)
   - Fix Import/Export not recognising correctly the imported services.
+  - Revoke button in Applications Settings underlines on hover.
 v 8.12.1
   - Fix a memory leak in HTML::Pipeline::SanitizationFilter::WHITELIST

app/views/doorkeeper/authorized_applications/_delete_form.html.haml

@@ -6,4 +6,4 @@
   
 = form_tag path do
   %input{:name => "_method", :type => "hidden", :value => "delete"}/
-  = submit_tag 'Revoke', onclick: "return confirm('Are you sure?')", class: 'btn btn-link btn-remove btn-sm'
+  = submit_tag 'Revoke', onclick: "return confirm('Are you sure?')", class: 'btn btn-remove btn-sm'