Fix typo

Author: Minty252

reverseString/README.md

@@ -1,6 +1,6 @@
 # Exercise 02 - Reverse a String.
 
-Pretty simple, write a function called `reverseString` that returns it's input, reversed!
+Pretty simple, write a function called `reverseString` that returns its input, reversed!
 
 ```javascript
 reverseString('hello there') // returns 'ereht olleh'