Fix off by one in the iterator documentation

`(1..100).map(|x| x + 1)` is actually mapping [1,100) to [2,101)

Author: stevegury

src/doc/trpl/iterators.md

@@ -259,7 +259,7 @@ a new iterator. The simplest one is called `map`:
 
 `map` is called upon another iterator, and produces a new iterator where each
 element reference has the closure it's been given as an argument called on it.
-So this would give us the numbers from `2-100`. Well, almost! If you
+So this would give us the numbers from `2-101`. Well, almost! If you
 compile the example, you'll get a warning:
 
 ```text