>>> Downloading 'https://mirror.dkm.cz/gentoo/distfiles/zsh-5.5.1.tar.gz'
--2018-04-17 17:25:36--  https://mirror.dkm.cz/gentoo/distfiles/zsh-5.5.1.tar.gz
Resolving mirror.dkm.cz... 2a02:8300:8000:3::49, 86.49.49.49
Connecting to mirror.dkm.cz|2a02:8300:8000:3::49|:443... connected.
ERROR: cannot verify mirror.dkm.cz's certificate, issued by ‘CN=Let's Encrypt Authority X3,O=Let's Encrypt,C=US’:
  Unable to locally verify the issuer's authority.
To connect to mirror.dkm.cz insecurely, use `--no-check-certificate'.
>>> Downloading 'https://www.zsh.org/pub/zsh-5.5.1.tar.gz'
--2018-04-17 17:25:37--  https://www.zsh.org/pub/zsh-5.5.1.tar.gz
Resolving www.zsh.org... 203.24.36.104
Connecting to www.zsh.org|203.24.36.104|:443... connected.
ERROR: cannot verify www.zsh.org's certificate, issued by ‘CN=Let's Encrypt Authority X3,O=Let's Encrypt,C=US’:
  Unable to locally verify the issuer's authority.
To connect to www.zsh.org insecurely, use `--no-check-certificate'.
!!! Couldn't download 'zsh-5.5.1.tar.gz'. Aborting.
 * Fetch failed for 'app-shells/zsh-5.5.1', Log file:
 *  '/var/tmp/portage/app-shells/zsh-5.5.1/temp/build.log'