Sync "Advanced Types.md"

[zhongsp]

Done.

[xcatliu]

type assertion
type predicate

这两个都翻译成类型断言可能会引起误解

[zhongsp]

@xcatliu 感谢 我稍后review一下

[mishengqiang]

@zhongsp type predicate是类型谓词，type assertion是类型断言。

[xcatliu]

贴一段上下文：

To get the same code working, we’ll need to use a type assertion:

let pet = getSmallPet();

if ((<Fish>pet).swim) {
    (<Fish>pet).swim();
}
else {
    (<Bird>pet).fly();
}

To define a type guard, we simply need to define a function whose return type is a type predicate:

function isFish(pet: Fish | Bird): pet is Fish {
    return (<Fish>pet).swim !== undefined;
}

pet is Fish is our type predicate in this example.