Tiny fix in the tutorial on default implicits
Tiny fix in the tutorial on default implicits

Fixed a tiny typo (`Z` => `n`)
kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev