Auto merge of #170 - miller-time:rename-iterator-exercise, r=komaeda

fix(iterators): Rename iterator3.rs

fixes #155

exercises/standard_library_types/iterators3.rs

@@ -1,4 +1,4 @@
-// iterator3.rs
+// iterators3.rs
 // This is a bigger exercise than most of the others! You can do it!
 // Here is your mission, should you choose to accept it:
 // 1. Complete the divide function to get the first four tests to pass