fix: package.json to reduce vulnerabilities
fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:hoek:20180212

Latest report for grawlinson/quick-epub:
https://snyk.io/test/github/grawlinson/quick-epub
grawlinson/quick-epub,grawlinson/quick-epub