Apply GitLab UI button styles to buttons in app/views/admin/hooks directory

app/views/admin/hooks/edit.html.haml

@@ -9,9 +9,9 @@
     = form_for @hook, as: :hook, url: admin_hook_path do |f|
       = render partial: 'form', locals: { form: f, hook: @hook }
       .form-actions
-        %span>= f.submit _('Save changes'), class: 'btn btn-success gl-mr-3'
+        %span>= f.submit _('Save changes'), class: 'btn gl-button btn-success gl-mr-3'
         = render 'shared/web_hooks/test_button', hook: @hook
-        = link_to _('Delete'), admin_hook_path(@hook), method: :delete, class: 'btn btn-remove float-right', data: { confirm: _('Are you sure?') }
+        = link_to _('Delete'), admin_hook_path(@hook), method: :delete, class: 'btn gl-button btn-remove float-right', data: { confirm: _('Are you sure?') }
 
     %hr
 

app/views/admin/hooks/index.html.haml

@@ -7,7 +7,7 @@
   .col-lg-8.gl-mb-3
     = form_for @hook, as: :hook, url: admin_hooks_path do |f|
       = render partial: 'form', locals: { form: f, hook: @hook }
-      = f.submit _('Add system hook'), class: 'btn btn-success'
+      = f.submit _('Add system hook'), class: 'btn gl-button btn-success'
 
     = render 'shared/web_hooks/index', hooks: @hooks, hook_class: @hook.class