Fix broken code in doc examples.
//! # fn iterate(mut cx: FunctionContext) -> JsResult<JsUndefined> {
//! let iterator = /* ... */; // iterator object
//! let next = iterator.get("next")? // iterator's `next` method
-//! .downcast::<JsFunction, _>(&mut cx)?;
+//! .downcast_or_throw::<JsFunction, _>(&mut cx)?;
//! let mut numbers = vec![]; // results vector
//! let mut done = false; // loop controller
//!
//! while !done {
//! done = cx.execute_scoped(|mut cx| { // temporary scope
-//! let obj = next.call(&mut cx, iterator, vec![])?; // temporary object
+//! let args: Vec<Handle<JsValue>> = vec![];
+//! let obj = next.call(&mut cx, iterator, args)?; // temporary object
//! let number = obj.get(&mut cx, "value")? // temporary number
-//! .downcast::<JsNumber, _>(&mut cx)?
+//! .downcast_or_throw::<JsNumber, _>(&mut cx)?
//! .value(&mut cx);
//! numbers.push(number);
//! Ok(obj.get(&mut cx, "done")? // temporary boolean
-//! .downcast::<JsBoolean, _>(&mut cx)?
+//! .downcast_or_throw::<JsBoolean, _>(&mut cx)?
//! value(&mut cx));
//! })?;
//! }
