coverage-worker flag path construction fix

[acsrlabs]

fixed the --coverage-worker of ziggy fuzz by changing the path construction so the correct path to the profraw files can be found.

fixes #171

[louismerlin]

Nice! Could you please add an e2e test? (which should fail on the previous version of the code)

[acsrlabs]

will do!

[chris-srlabs]

Nice! Could you please add an e2e test? (which should fail on the previous version of the code)

Something like cargo ziggy fuzz --coverage-worker --coverage-interval=0 --corpus-sync-interval=0 for the url example seems to work as an e2e test.

[louismerlin]

Cool thank you @acsrlabs, and thank you @chris-srlabs for getting this through the finish line!