clean: change return value

src/main.c

@@ -64,7 +64,7 @@ range_error:
 
 value_error:
     print_err("invalid argument: in '%s' '%c' is not a digit", str, *start);
-    return 1;
+    return 2;
 }
 
 static int get_setting(char * const *av, struct setting *setting)