fix to the random-world flag

src/main.rs

@@ -250,9 +250,9 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let raw_conf = open_file(matches.value_of("file").unwrap_or("two_robots.txt"))?;
 
     let mut robot_pool: Vec<robot::Robot> = Vec::new();
-    let world: world::World = match matches.value_of("random-world") {
-        None => parse_config(raw_conf, &mut robot_pool)?,
-        Some(_) => world::random_world(),
+    let world: world::World = match matches.is_present("random-world") {
+        false => parse_config(raw_conf, &mut robot_pool)?,
+        true => world::random_world(),
     };
 
     let mut hash: HashMap<robot::Position, u32> = HashMap::new();