what-is-fp: adjust code

Author: fabianhjr

src/pages/intro/what-is-fp.md

@@ -30,7 +30,7 @@ In my view functional programming is not about immutability, or keeping to "the
 ```scala mdoc:silent
 def sum(numbers: List[Int]): Int = {
   var total = 0
-  numbers.foreach(x => total = total + x)
+  numbers foreach { x => total = total + x }
   total
 }
 ```
@@ -50,7 +50,7 @@ val it2 = Iterator(1, 2, 3, 4)
 ```
 
 ```scala mdoc
-it.zip(it2).next()
+(it zip it2).next()
 ```
 
 However if we pass the same generator twice we get a surprising result.
@@ -60,7 +60,7 @@ val it3 = Iterator(1, 2, 3, 4)
 ```
 
 ```scala mdoc
-it3.zip(it3).next()
+(it3 zip it3).next()
 ```
 
 The usual functional programming solution is to avoid mutable state but we can envisage other possibilities. For example, an [effect tracking system][effect-system] would allow us to avoid combining two generators that use the same memory region. These systems are still research projects, however.