fixed if let guards documentation

Author: Kivooeo

src/expressions/match-expr.md

@@ -171,7 +171,6 @@ When the pattern matches successfully, the `if let` expression in the guard is e
   * Otherwise, the next arm is tested.
 
 ```rust
-#![feature(if_let_guard)]
 let value = Some(10);
 
 let msg = match value {
@@ -195,7 +194,7 @@ match opt {
         println!("x = {}, y = {}", x, y);
     }
     _ => {
-        // `y` is not available here — it was only bound inside the guard above.
+        // `y` is not available here --- it was only bound inside the guard above.
         // Uncommenting the line below will cause a compile-time error:
         // println!("{}", y); // error: cannot find value `y` in this scope
     }
@@ -229,7 +228,7 @@ Before a guard (including an `if let` guard) is evaluated:
       };
 
       ```
-      In the above example, `v` is already bound in the outer pattern, and the guard attempts to move it — this is not allowed. You can fix it by cloning or borrowing:
+      In the above example, `v` is already bound in the outer pattern, and the guard attempts to move it --- this is not allowed. You can fix it by cloning or borrowing:
       ```rust
       Some(v) if let Some(_) = take(v.clone()) => "ok",
       ```