`description` is defined on `any`
`description` is defined on `any`

Fixes small omission to make the heading for `description()` match the headers for the methods around it.
pandeysoni/joi,naitsric/joi,bananaoomarang/joi,olistic/joi-extended,davidbenko9/joi,lloydbenson/joi,pikselpalette/joi,jeffbski/joi,myndzi/joi,jagoda/joi,myndzi/joi,geminiyellow/joi,opyate/joi,danielb2/joi,thethanghn/react-native-joi,cesarmarinhorj/joi,tpiecora/joi,rmoorman/joi,robertherber/joi-extended,ck-lee/joi