explainer: Fix badCallback example, throws only if iterable has items (#15)

In order to match the current specification and to be consistent with Array.from. `Array.from([], ()=>{throw 1})` will not throw but `Array.from([1], ()=>{throw 1})` will.

Author: senocular

README.md

@@ -187,7 +187,7 @@ Array.fromAsync(badIterable);
 Array.fromAsync(genError());
 Array.fromAsync(genRejection());
 Array.fromAsync(genErrorAsync());
-Array.fromAsync([], badCallback);
+Array.fromAsync([1], badCallback);
 BadConstructor.call(Array.fromAsync, []);
 // These create promises that will reject with TypeErrors.
 Array.fromAsync(null);