Fix a doctest to run on 7.4.2 with an old version of ByteString
Fix a doctest to run on 7.4.2 with an old version of ByteString

cdepillabout/lens,timjb/lens,Fuuzetsu/lens,hvr/lens,hvr/lens,rpglover64/lens,cchalmers/lens,danidiaz/lens,ddssff/lens,Gabriel439/lens,Icelandjack/lens,omefire/lens