Upgrade concurrency-kit to 0.4.1

This includes a breaking api change for ck_ring (introduced in ck
0.3.3). Applications that use both libphenom and ck_ring will need to
modify their use of ck_ring.
Fixup travis build for CK upgrade

Bump the CK version that we pull in for travis builds.

Can't use unlikely in this code branch, because the code branch is already
unlikely and the code size would grow:

```
thirdparty/ck/include/ck_ring.h:243:1: error: inlining failed in call to 'ck_ring_enqueue_spmc': call is unlikely and code size would grow [-Werror=inline]
corelib/job.c:539:12: error: called from here [-Werror=inline]
```