fix(logging): remove spaces from logging op name in the worker

After the switch to mozlog, the first arg to all logging calls is an
"op name" which cannot contain spaces.  This removes one such instance
which was causing (unhandled) errors in the worker process.

Closes #77
Merge pull request #78 from mozilla/rfk/fix-worker-logging-error

fix(logging): remove spaces from logging op name in the worker