Fixes issue guard#213

- Changes in dsl.rb fixes the issue.
- Changes in dsl_describer.rb allows to show the '*' when using symbols
as guard names instead of strings (for example: guard :spark)

lib/guard/dsl.rb

@@ -101,7 +101,7 @@ def evaluate_guardfile(options = {})
         fetch_guardfile_contents
         instance_eval_guardfile(guardfile_contents_with_user_config)
 
-        UI.error 'No guards found in Guardfile, please add at least one.' if !::Guard.guards.nil? && ::Guard.guards.empty?
+        UI.error 'No guards found in Guardfile, please add at least one.' if ::Guard.guards.nil? && ::Guard.guards.empty?
       end
 
       # Re-evaluate the `Guardfile` to update the current Guard configuration.

lib/guard/dsl_describer.rb

@@ -48,7 +48,7 @@ def list(options)
         evaluate_guardfile(options)
 
         installed_guards = guardfile_structure.inject([]) do |installed, group|
-          group[:guards].each { |guard| installed << guard[:name] } if group[:guards]
+          group[:guards].each { |guard| installed << guard[:name].to_s } if group[:guards]
           installed
         end