Update index.md

Fix where "word" was used instead of "character", and fix one typo.

Author: blakegarretson

chapters/strings/reverse/index.md

@@ -3,7 +3,7 @@ title: Reversing a String by Word or Character
 question: How do I reverse a string by word or character?
 ---
 
-Reversing a string by word is very similar to the process to reverse an array.  The difference is that strings are immutable in Go.  Therefor, we must first convert the string to a mutable array of runes (`[]rune`), perform the reverse operation on that, and then re-cast to a string.
+Reversing a string by character is very similar to the process to reverse an array.  The difference is that strings are immutable in Go.  Therefore, we must first convert the string to a mutable array of runes (`[]rune`), perform the reverse operation on that, and then re-cast to a string.
 
 {% include example.html example="reverse_by_character" %}