Import monoid to fix errors with latest optparse-applicative 0.13.*
Import monoid to fix errors with latest optparse-applicative 0.13.*

sordina/wai,sordina/wai,creichert/wai,tolysz/wai,sordina/wai,tolysz/wai,kazu-yamamoto/wai,sordina/wai,kazu-yamamoto/wai,tolysz/wai,yesodweb/wai,yesodweb/wai,creichert/wai,tolysz/wai