fix(notes): Minor typo on note 1

[arjunnaha]

Fix a very minor typo

# let even_digit n =
    match n with
    | 0 -> true
    | 2 -> true
    | 4 -> true
    | 6 -> true
    | 8 -> true
    | _ -> false;;
val even_digit : int -> bool = <fun>

The patterns here, save the last one, are just integer literals. If n is the same as any of these integers, the value true is produced. The last case uses a "wildcard," which matches anything and produces true false.