Explicitly add dependency on istanbul-lib-hook and istanbul-lib-instrument

This addresses the problem reported here: !21 (comment 1480266957)

Summary

Add the dependency on istanbul-lib-hook and istanbul-lib-instrument, as seen in the file src/worker.ts, to the package manifest.

Description

Previously these dependency appeared in the dependency tree due to this project's dependency on nyc. First, explicitly defining project dependencies is a good idea in and off itself because it avoids problems if all direct dependencies drop the implicit dependency (not considered a breaking change). Second, the version of istanbul-lib-instrument that v15 of nyc depends on is incompatible with its usage in this project (evidenced by unexpected logging when fuzzing starts) - specifying the actual version (range) this project depends on fixes that problem.