bump to version 2.8.0
bump to version 2.8.0

graingert/premailer,industrydive/premailer,lavr/premailer,lavr/premailer,peterbe/premailer,graingert/premailer,kengruven/premailer,ionelmc/premailer,ionelmc/premailer,peterbe/premailer,industrydive/premailer,peterbe/premailer,kengruven/premailer