Fix example's crash (#16)

[ales-tsurko]

Fixes #16
Possibly related to #17 No, it isn't

[ales-tsurko]

The cause of the crash is related to simple-log crate. I tried SimpleLogger without initialization of a file and it still crashes. But switching to another library (simple-logging, for ex.) fixes the problem.

Checked with log4rs — crashes too.

There is unwrap on mutex in Log trait implementation in simple-log. simple-logging makes it more safe, but it possibly just doesn't work sometimes, because it doesn't handle errors... Anyway it's fine for a log example and out of scope for the library.