Yarn: Installation Problem: [title]

[behzodjon]

Which operating system are you using:
Ubuntu 16.04

Please describe the steps you took when trying to install Yarn and what went wrong:
unable to install yarn

[traceypooh]

confirmed - please fix! :)
seems like your key expired? (if so, happy new year ;-)

docker run --rm -it ubuntu:xenial bash -c '( apt-get update && apt-get -y upgrade && apt-get -y install curl apt-transport-https add-apt-key && curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg |apt-key add - && echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list && apt-get update ) || bash'

Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [107 kB]
...
Setting up add-apt-key (1.0-0.5) ...
Setting up curl (7.47.0-1ubuntu2.11) ...
Processing triggers for libc-bin (2.23-0ubuntu10) ...
Processing triggers for ca-certificates (20170717~16.04.1) ...
Updating certificates in /etc/ssl/certs...
148 added, 0 removed; done.
Running hooks in /etc/ca-certificates/update.d...
done.
OK
deb https://dl.yarnpkg.com/debian/ stable main
Get:1 https://dl.yarnpkg.com/debian stable InRelease [13.3 kB]
Hit:2 http://security.ubuntu.com/ubuntu xenial-security InRelease              
Hit:3 http://archive.ubuntu.com/ubuntu xenial InRelease                  
Ign:1 https://dl.yarnpkg.com/debian stable InRelease
Get:4 https://dl.yarnpkg.com/debian stable/main amd64 Packages [8168 B]
Hit:5 http://archive.ubuntu.com/ubuntu xenial-updates InRelease                  
Get:6 https://dl.yarnpkg.com/debian stable/main all Packages [8168 B]            
Hit:7 http://archive.ubuntu.com/ubuntu xenial-backports InRelease              
Fetched 29.7 kB in 0s (32.9 kB/s)                 
Reading package lists... Done
W: GPG error: https://dl.yarnpkg.com/debian stable InRelease: The following signatures were invalid: KEYEXPIRED 1507181400  KEYEXPIRED 1546376218  KEYEXPIRED 1546372003  KEYEXPIRED 1546372003  KEYEXPIRED 1507181400  KEYEXPIRED 1546376218  KEYEXPIRED 1546372003  KEYEXPIRED 1507181400  KEYEXPIRED 1546376218  KEYEXPIRED 1546372003
W: The repository 'https://dl.yarnpkg.com/debian stable InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

[ElectronicWar]

Same issue with Debian repository, GPG key is expired

[Daniel15]

Will track this in #6865