Fix keyword style for worker

Just came across this particular problem (parsing will fail with invalid params).

As the reader might remember we changed the original layout on request as part of pull-request
#750 (for #685), because we did not want calls like this `perform(1, ...` as the reader might not know what
the `1` stands for. So we used keyword args: `perform(try_count: 1, ...`. However this results in some problems now. These two commits should fix the problem.

However we could also go back to the old solution and just use a constant to explain the `1`.
For example: `INITIAL_TRY_COUNT = 1` which would allow us this call: `perform(INITIAL_TRY_COUNT, ...`.