Fix Elixir 1.16 warnings

[axelson]

• Fixes Logger.warn deprecation (requires bump to Elixir 1.11 which was released on 2020-10-06)
• ssl_verify_fun 1.1.6 doesn't compile under Elixir 1.16
• Remove applications definition and instead only use extra_applications
  • Fixes this warning "both :extra_applications and :applications was found in your mix.exs. You most likely want to remove the :applications key, as all applications are derived from your dependencies"
  • Also the applications listed in apps were just the normal dependencies (and logger)

The only functional change here is upgrading the minimum supported version of Elixir

[yordis]

fixed

[axelson]

yay! Thank you @yordis!