NSelect prop fallback-option's better type hint

[sigmarising]

This function solves the problem (这个功能解决的问题)

Help make dev with vscode better.

Expected API (期望的 API)

The offical docs show that fallback-option's type is false | (value: string | number) => SelectOption

But actually I found in .d.ts file is (value: string | number) => false | SelectOption, which made the vscode give me an type error when I put the false value into the prop.

However, even vscode give me this error, I can still compile my code and run it successfully.

[07akioni]

This is a bug, I'll fix it.