atbash-cipher: Correct capitalization of 'atbash' to 'Atbash' in instructions

Author: tasxatzial

exercises/atbash-cipher/description.md

@@ -1,6 +1,6 @@
 # Description
 
-Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
+Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.
 
 The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards.
 The first letter is replaced with the last letter, the second with the second-last, and so on.