Update functions.md

There was a little grammatical error in this section.
I modified: `DON'T let `println!` works` to `DON'T let `println!` work`

en/src/basic-types/functions.md

@@ -35,7 +35,7 @@ fn print() -> i32 {
 
 ```rust,editable
 // Solve it in two ways
-// DON'T let `println!` works
+// DON'T let `println!` work
 fn main() {
     never_return();
 
@@ -98,4 +98,4 @@ fn main() {
 }
 ```
 
-> You can find the solutions [here](https://github.com/sunface/rust-by-practice/blob/master/solutions/basic-types/functions.md)(under the solutions path), but only use it when you need it
+> You can find the solutions [here](https://github.com/sunface/rust-by-practice/blob/master/solutions/basic-types/functions.md)(under the solutions path), but only use it when you need it