Add and apply Style/HashConversion rubocop rule

This rule was added in Rubocop 1.10.0. This style is IMHO clearer and
possible since Ruby 2.1.

.rubocop.yml

@@ -469,6 +469,9 @@ Style/ClassVars:
 Style/CollectionMethods:
   Enabled: true
 
+Style/HashConversion:
+  Enabled: true
+
 Style/HashSyntax:
   Enabled: true
 

app/helpers/settings_helper.rb

@@ -13,7 +13,7 @@ module SettingsHelper
   end
 
   def setting
-    @all_settings ||= Hash[Setting.all.map { |s| [s.key, s.value.presence] }]
+    @all_settings ||= Setting.all.map { |s| [s.key, s.value.presence] }.to_h
   end
 
   def display_setting_name(setting_name)