docs(examples): Remove unnecessary error check

Rather not confuse the point for users.

examples/13_enum_values.rs

@@ -42,7 +42,8 @@ fn main() {
         .get_matches();
 
     // Note that you don't have to specify the type since rustc can infer it for you
-    let t = m.value_of_t("type").unwrap_or_else(|e| e.exit());
+    // It's safe to call unwrap because the value is required and clap will report an error for us.
+    let t = m.value_of_t("type").unwrap();
 
     // Now we can use our enum like normal.
     match t {