Fix docstring for `mul`
Fix docstring for `mul`

sgebbie/ponyc,kulibali/ponyc,jemc/ponyc,ponylang/ponyc,cquinn/ponyc,dipinhora/ponyc,dipinhora/ponyc,jemc/ponyc,ponylang/ponyc,sgebbie/ponyc,kulibali/ponyc,cquinn/ponyc,ponylang/ponyc,cquinn/ponyc,kulibali/ponyc,kulibali/ponyc,cquinn/ponyc,jemc/ponyc,sgebbie/ponyc,sgebbie/ponyc,dipinhora/ponyc,sgebbie/ponyc