Bug: If link # changes then the link does not update

[niftylettuce]

For example, if you start off with:

#123

It becomes

[#123](https://github.com/wooorm/remark-github/issues/123)

However if you change the issue number it still has the same inaccurate link:

[#456](https://github.com/wooorm/remark-github/issues/123)

[Titus]

GitHub doesn’t change the link either, and allows that:

[#123](https://github.com/wooorm/remark-github/issues/123)
[#456](https://github.com/wooorm/remark-github/issues/123)

Yields:

#123
#456

[Titus]

This is a feature, not a bug.