Logger backends uses deprecated :warn instead of :warning

[vkryukov]

Hello,

I noticed a small annoyance when developing a custom logger backend: a warning message about deprecated usage of :warn is produced. It can be illustrated by the following code:

victor@Mac ~/s/logger_default_handler (main)> mix run lib/logger_default_handler.exs
warning: the log level :warn is deprecated, use :warning instead
  (logger 1.17.3) lib/logger.ex:1178: Logger.elixir_level_to_erlang_level/1
  (logger 1.17.3) lib/logger.ex:635: Logger.compare_levels/2
  (logger_backends_sql 0.1.0) lib/logger_backends_sql.ex:122: LoggerBackends.SQL.meet_level?/2
  (logger_backends_sql 0.1.0) lib/logger_backends_sql.ex:79: LoggerBackends.SQL.handle_event/2
  (stdlib 6.1.2) gen_event.erl:1921: :gen_event.server_update/4
  (stdlib 6.1.2) gen_event.erl:1903: :gen_event.server_notify/4


11:14:19.305 [warning] This is a warning message

11:14:19.305 [error] This is an error message
You should see that unconditionally
victor@Mac ~/s/logger_default_handler (main)> 

The culprit is this line, and the fix is really a one-liner which I will do in a pull request.