Resolve more linter warnings

src/parser.rs

@@ -33,7 +33,7 @@ fn scan(code: &str, mut ix: usize, mut tokens: Tokens) -> Tokens {
         return tokens;
     }
 
-    let c: char = code[ix..ix + 1].chars().next().unwrap();
+    let c: char = code[ix..].chars().next().unwrap();
     if c.is_ascii_alphanumeric() || SPECIAL_CHARS.contains(&c) {
         return scan_identifier(code, ix, tokens);
     }