error code doc change

Author: arora-aman

compiler/rustc_error_codes/src/error_codes/E0504.md

@@ -7,20 +7,20 @@ Erroneous code example:
 
 ```compile_fail
 struct FancyNum {
-    num: u8,
+    s: String,
 }
 
 fn main() {
-    let fancy_num = FancyNum { num: 5 };
+    let fancy_num = FancyNum { s: "".into() };
     let fancy_ref = &fancy_num;
 
     let x = move || {
-        println!("child function: {}", fancy_num.num);
+        println!("child function: {}", fancy_num.s);
         // error: cannot move `fancy_num` into closure because it is borrowed
     };
 
     x();
-    println!("main function: {}", fancy_ref.num);
+    println!("main function: {}", fancy_ref.s);
 }
 ```