Fix typo in useremail

[peili]

No description provided.

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[samtstern]

useremail already exists as a const above, so we'll have to use a new variable name.

[peili]

@samtstern Then I'd suggest to be consistent with the other examples and reduce it to a single const at the top of the file? Well, I see the documentation uses different snippets of this file, so that doesn't help either.
We could wrap the code snippets in a function to allow different scopes to declare the same const.
(I don't know if that would break the [START sign_in_with_email_link] parsing)

() => {
// [START sign_in_with_email_link]
// Admin SDK API to generate the sign in with email link.
const useremail = 'user@example.com';
....
// [END sign_in_with_email_link]
}

https://firebase.google.cn/docs/auth/admin/email-action-links?hl=EN-GB

[samtstern]

@peili yes I think you're right that one function per snippet would be the better approach, just like we do over here:
https://github.com/firebase/snippets-web/blob/master/functions/callable.js#L17

[peili]

@googlebot I signed it!

[thatfiredev]

@peili I went ahead and wrapped the code inside a function so that we can get this merged.

Thank you for your contribution!