Simplify Kleisli example

Amended second instance of parseAndReciprocal to use the same functions as in the earlier example.

docs/src/main/tut/datatypes/kleisli.md

@@ -77,9 +77,9 @@ Returning to our earlier example:
 // Bring in cats.FlatMap[Option] instance
 import cats.implicits._
 
-val parse = Kleisli((s: String) => try { Some(s.toInt) } catch { case _: NumberFormatException => None })
+val parse = Kleisli((s: String) => if (s.matches("-?[0-9]+")) Some(s.toInt) else None)
 
-val reciprocal = Kleisli((i: Int) => if (i == 0) None else Some(1.0 / i))
+val reciprocal = Kleisli((i: Int) => if (i != 0) Some(1.0 / i) else None)
 
 val parseAndReciprocal = reciprocal.compose(parse)
 ```