fix dialyzer failures.

[jimsynz]

Hi there.

Running dialyzer on an Elixir project which has emqtt as a dependency results in the following dialyzer failures:

< path redacted >deps/emqtt/src/emqtt.erl:137:42:unknown_type
Unknown type: :emqx_types.message/0.
________________________________________________________________________________
< path redacted >deps/emqtt/src/emqtt.erl:151:31:unknown_type
Unknown type: :ssl.ssl_option/0.
________________________________________________________________________________
done (warnings were emitted)
Halting VM with exit status 2

The SSL one is easy to fix - there is no ssl:ssl_option (or at least not anymore), but there is ssl:tls_option.

The other failure is because the emqx_types module doesn't exist. I found it inside the emqx app source, but emqx is not listed as a project dependency. I'm open to suggestions on how to fix that.

[zmstone]

thank you @jimsynz
could you try to keep the compatibility with old version otp?

[jimsynz]

@zmstone I'm not sure that it's possible.

[zmstone]

@zmstone I'm not sure that it's possible.

-if(?OTP_RELEASE < 27).
-type tls_options() :: [ssl:tls_option()].
-else.
-type tls_options() :: [ssl:ssl_option()].
-endif.

[jimsynz]

Aha! This is why we don't get Elixirists to write Erlang :)

I'll update the PR.

[jimsynz]

@zmstone good to go for your review. Cheers!

[zmstone]

need same fix here ?