LetsEncrypt-DNS 2.11.0

Added

• Environment variable LETSENCRYPT_SKIP_REGISTER (default: false) can be set to true and avoid the container
  to try to register a new account against Let'sEncrypt servers: useful for instance if the container is already
  attached to a letsencrypt configuration folder with an existing account.
• By modifying the run.sh script, the container now responds to interruption signals and proceed to shutdown by
  itself, without the need from the Docker daemon to kill it.

Modified

• Update Lexicon to 3.2.1 (various fixes)
• Update Certbot to 0.33.1 (various fixes)