fix(exercises): adding question mark to quiz2

Question marks added for consistency.

closes #496

Author: Ant0wan

exercises/quiz2.rs

@@ -17,14 +17,14 @@ fn string(arg: String) {
 }
 
 fn main() {
-    ("blue");
-    ("red".to_string());
-    (String::from("hi"));
-    ("rust is fun!".to_owned());
-    ("nice weather".into());
-    (format!("Interpolation {}", "Station"));
-    (&String::from("abc")[0..1]);
-    ("  hello there ".trim());
-    ("Happy Monday!".to_string().replace("Mon", "Tues"));
-    ("mY sHiFt KeY iS sTiCkY".to_lowercase());
+    ???("blue");
+    ???("red".to_string());
+    ???(String::from("hi"));
+    ???("rust is fun!".to_owned());
+    ???("nice weather".into());
+    ???(format!("Interpolation {}", "Station"));
+    ???(&String::from("abc")[0..1]);
+    ???("  hello there ".trim());
+    ???("Happy Monday!".to_string().replace("Mon", "Tues"));
+    ???("mY sHiFt KeY iS sTiCkY".to_lowercase());
 }