`npm run start:lighthouse:junit-headless` sometimes hangs

[andymsuk]

Summary

npm run start:lighthouse:junit-headless sometimes hangs and doesn't exit

Expected Behaviour

npm run start:lighthouse:junit-headless will finish successfully or unsuccessfully and exit every time.

Current Behaviour

npm run start:lighthouse:junit-headless sometimes hangs and doesn't exit

Possible Solution

Might be fixed by #26

Environment

Seen on our Jenkins and on some Macbooks