fix docs code block for `makeClassyPrisms`
fix docs code block for `makeClassyPrisms`

The second code block in documentation for `makeClassyPrisms` doesn't render correctly. See e.g. [hackage docs](http://hackage.haskell.org/package/lens-4.5/docs/Control-Lens-TH.html#v:makeClassyPrisms).
ddssff/lens,Gabriel439/lens,Icelandjack/lens,Fuuzetsu/lens,timjb/lens,cchalmers/lens,omefire/lens,rpglover64/lens,cdepillabout/lens,danidiaz/lens