Update ruby-listen to 3.0.8, latest 3.0.x release.

v3.0.7

Backports

* #385 - backport #383 (allow stopping when not fully initialized)

v3.0.8

Bugfixes:

* prevent crash when stopping uninitialized listener 2c78999
* prevent crash when stopping uninitialized adapter 8b06d2c
* #392 - Change rb-fsevent dependency to work on OS X 10.6-10.8
* get JRuby to fail with ENOTDIR like MRI does c3a8cbb
* avoid unkillable thread problem on JRuby e86dccf
* explicitly require forwardable (in case of further backports) 51d7706

(taca)