Fix compatibility with Symfony

[enumag]

Currently I'm getting this error:

User Deprecated: The "Tracy\Logger::defaultMailer()" method is considered internal. It may change without further notice. You should not extend it from "Nella\MonologTracy\Tracy\LoggerHelper".

it is thrown by Symfony DebugClassLoader here.

It is not necessary to override this method. The default implementation internally calls formatMessage which will throw an exception anyway.

[mhujer]

Thanks!

[mhujer]

I just tagged a new version: 2.0.2