Ensure group name is a Symbol in Guard::Guard#initialize

lib/guard/guard.rb

@@ -19,7 +19,7 @@ module Guard
     # @param [Hash] options the custom Guard options.
     #
     def initialize(watchers = [], options = {})
-      @group = options.delete(:group) || :default
+      @group = options[:group] ? options.delete(:group).to_sym : :default
       @watchers, @options = watchers, options
     end
 
@@ -85,4 +85,5 @@ module Guard
     end
 
   end
+
 end