Chapter 4 - env_logger default format change causes difference from book

[louy2]

env_logger changed the default formatter to show target instead of module_path in version 0.9.0, which has caused the trace-level log showing the entering and exiting of spans to show

[.. TRACE tracing::span::active] -> Adding a new subscriber.

instead of

[.. TRACE zero2prod] -> Adding a new subscriber.

I probably should not have spent so much time finding the cause of this issue but here I am lol, might as well write it down for reference.