Fix typo

src/main.rs

@@ -21,7 +21,7 @@ fn parse_args() -> String {
     let mut args: Vec<String> = env::args().collect();
 
     if args.len() < 2 {
-        panic!("Must supply an string to encode");
+        panic!("Must supply a string to encode");
     }
 
     args.remove(1)