NPM audit vulnerabilities

[joepaquette]

Cloned the current master branch and found the following npm audit results:
`
.../FHIR.js$ npm audit

            === npm audit security report ===

// Run npm install --save-dev webpack@4.29.2 to resolve 3 vulnerabilities
SEMVER WARNING: Recommended action is a potentially breaking change
│ Low │ Prototype Pollution
│ Package │ lodash
│ Dependency of │ webpack [dev]
│ Path │ webpack > async > lodash
│ More info │ https://nodesecurity.io/advisories/577

│ Low │ Prototype Pollution
│ Package │ lodash
│ Dependency of │ webpack [dev]
│ Path │ webpack > watchpack > async > lodash
│ More info │ https://nodesecurity.io/advisories/577

│ Low │ Cryptographically Weak PRNG
│ Package │ randomatic
│ Dependency of │ webpack [dev]
│ Path │ webpack > watchpack > chokidar > anymatch > micromatch >
│ │ braces > expand-range > fill-range > randomatic
│ More info │ https://nodesecurity.io/advisories/157

// Run npm update lodash --depth 4 to resolve 1 vulnerability
│ Low │ Prototype Pollution
│ Package │ lodash
│ Dependency of │ typedoc [dev]
│ Path │ typedoc > handlebars > async > lodash
│ More info │ https://nodesecurity.io/advisories/577

found 4 low severity vulnerabilities in 1119 scanned packages
run npm audit fix to fix 1 of them.
3 vulnerabilities require semver-major dependency updates.
`

Installing the latest NPM release (4.7) currently triggers a High NPM audit warning due to another weakness in lodash:

┌───────────────┬──────────────────────────────────────────────────────────────┐
│ High          │ Prototype Pollution                                          │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ lodash                                                       │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Patched in    │ >=4.17.12                                                    │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ fhir                                                         │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ fhir > lodash                                                │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://npmjs.com/advisories/1065                            │