Update the metadata blurb to swap Caeser for Vigenère

Author: IsaacG

exercises/simple-cipher/metadata.toml

@@ -1,4 +1,4 @@
 title = "Simple Cipher"
-blurb = "Implement a simple shift cipher like Caesar and a more secure substitution cipher."
+blurb = "Implement the Vigenère cipher, a simple substitution cipher."
 source = "Substitution Cipher at Wikipedia"
 source_url = "https://en.wikipedia.org/wiki/Substitution_cipher"