Compile error with latest libcork

The libcork `cork_thread_get_id` function has been renamed to `cork_current_thread_get_id` as part of redjack/libcork#36.  So now we get a compile error in clogger:

```
/home/dcreager/git/clogger/src/libclogger/stream.c: In function ‘clog_stream_handler_claim’:
/home/dcreager/git/clogger/src/libclogger/stream.c:43:5: error: too few arguments to function ‘cork_thread_get_id’
In file included from /usr/include/libcork/threads.h:17:0,
                 from /home/dcreager/git/clogger/src/libclogger/stream.c:17:
/usr/include/libcork/threads/basics.h:73:1: note: declared here
make[2]: *** [src/CMakeFiles/libclogger.dir/libclogger/stream.c.o] Error 1
```