Upgrade dependencies

npm audit gives
```
found 46 vulnerabilities (21 low, 19 moderate, 5 high, 1 critical) in 6373 scanned packages
39 vulnerabilities require semver-major dependency updates.
7 vulnerabilities require manual review. See the full report for details.
```

The one critical vulnerability is
```
Critical Command Injection
Package growl
Dependency of mocha [dev]
Path mocha > growl
More info https://nodesecurity.io/advisories/146
```
This requires growl to be greater than version 1.10.2, which requires mocha to be at least 4.0.1. Currently mocha 3.1.2 is being used.