fix a compile error in iter_any.md (#1576)

src/fn/closures/closure_examples/iter_any.md

@@ -15,7 +15,7 @@ pub trait Iterator {
         // `FnMut` meaning any captured variable may at most be
         // modified, not consumed. `Self::Item` states it takes
         // arguments to the closure by value.
-        F: FnMut(Self::Item) -> bool {}
+        F: FnMut(Self::Item) -> bool;
 }
 ```