IsNan instead of IsNaN

[GoPapaSmurf]

Hello,

On p.75, section "Chapter 2 - Speaking C# → Working with variables → Storing real numbers → Comparing double and decimal types", in the last paragraph, there is a spelling mistake, it is written IsNan instead of IsNaN:

They also have methods for checking for these special values like IsInfinity and IsNan.

[markjprice]

Thanks! I have added an errata item for this issue: https://github.com/markjprice/cs11dotnet7/blob/main/docs/errata/errata.md#page-75---comparing-double-and-decimal-types