Fix ENOAUDIT error during npm audit

[jumde]

CI often fails with

Your configured registry (https://registry.npmjs.org/) does not support audit requests, or the audit endpoint is temporarily unavailable.

Figure out a way to get around this.

[mbacchi]

The audit deps script runs npm audit with some arguments one single time only. We could do some error handling here and if the Popen result is not 0, or we can detect the the audit endpoint is temporarily unavailable error message, we could sleep and retry a certain number of times. I'd recommend 3 retries for at least a total of 30 seconds in order to attempt to work around an isolated overloaded NPM registry endpoint.

This is also something that could fix Travis CI issues not just our CI build itself.