Fix Rubocop offenses

Signed-off-by: Rémy Coutable <remy@rymai.me>

app/helpers/audit_events_helper.rb

@@ -7,7 +7,7 @@ module AuditEventsHelper
     if key.match(/^(author|target)_.*/)
       ""
     else
-      "#{key.to_s} <strong>#{value}</strong>"
+      "#{key} <strong>#{value}</strong>"
     end
   end
 end

app/helpers/tree_helper.rb

@@ -155,7 +155,7 @@ module TreeHelper
   def disabled_lock_link(label, title, html_options)
     html_options['data-toggle'] = 'tooltip'
     html_options[:title] = title
-    html_options[:class] = "#{html_options[:class].to_s} disabled has-tooltip"
+    html_options[:class] = "#{html_options[:class]} disabled has-tooltip"
 
     content_tag :span, label, html_options
   end
@@ -163,7 +163,7 @@ module TreeHelper
   def enabled_lock_link(label, title, html_options)
     html_options['data-toggle'] = 'tooltip'
     html_options[:title] = title
-    html_options[:class] = "#{html_options[:class].to_s} has-tooltip"
+    html_options[:class] = "#{html_options[:class]} has-tooltip"
 
     link_to label, '#', html_options
   end