Add the option for the gamma cipher.

src/cipher_analytical_machine/cli/options.clj

@@ -22,7 +22,7 @@
     (option-values-as-list option values)))
 
 (def cipher-options
-  #{"Caesar" "Simple substitution and Caesar"})
+  #{"Caesar" "Simple substitution and Caesar" "Gamma"})
 
 (def default-cipher "Caesar")