Checklist

• This is a plugin issue and not a different kind of issue
• I have read the contribution guidelines
• I have checked the list of open and recently closed plugin issues
• I have checked the commit log of the master branch

Streamlink version

Latest build from the master branch

Description

The niconico function using login is broken. This error is shown:
404 Client Error: Not Found for url: https://account.nicovideo.jp/

The plugin seems to be pointing to https://account.nicovideo.jp/login/redirector which does not work anymore.
Pointing to https://account.nicovideo.jp/login instead should solve the issue.

Debug log

Used syntax:
streamlink -o "output.ts" https://live.nicovideo.jp/watch/[video-ID] best --niconico-email [mailaddress] --niconico-password [PW]