Regenerate gemspec for version 0.4.0
Regenerate gemspec for version 0.4.0

firmanm/impressionist,guodongme/impressionist,guodongme/impressionist,samchen2009/impressionist,firmanm/impressionist,guodongme/impressionist,firmanm/impressionist,charlotte-ruby/impressionist,charlotte-ruby/impressionist,charlotte-ruby/impressionist,samchen2009/impressionist,samchen2009/impressionist