Rewatch: lock file not cleaned up

[cknitt]

If an error occurs when initializing the build, the generated lock file is not cleaned up.

E.g., when I run ./cli/rescript.js build in the project root, I get

[1/7] 📦 Building package tree...Could not initialize build. Error: No such file or directory (os error 2)

and the lock file is left behind.

[cknitt]

Ok, sorry, I misunderstood how the lockfile mechanism works.

/* This locking mechanism is meant to never be deleted. Instead, it stores the PID of the process
 * that's running, when trying to aquire a lock, it checks wether that process is still running. If
 * not, it rewrites the lockfile to have its own PID instead. */