Upgrade all dependencies

[andyjdavis]

When I did 'npm install' in this repository I got a nasty warning about there being 4 low and 1 high priority vulnerabilities. It may or may not be important given the nature of the code in here but I thought it worth tidying up.

Running 'npm audit' produced this

# npm audit report

bl  <=1.2.2 || 2.0.1 - 2.2.0 || 3.0.0 || 4.0.0 - 4.0.2
Severity: high
Remote Memory Exposure - https://npmjs.com/advisories/1555
fix available via `npm audit fix`
node_modules/bl

lodash  <4.17.19
Prototype Pollution - https://npmjs.com/advisories/1523
fix available via `npm audit fix`
node_modules/lodash

minimist  <0.2.1 || >=1.0.0 <1.2.3
Prototype Pollution - https://npmjs.com/advisories/1179
fix available via `npm audit fix --force`
Will install mocha@8.3.2, which is a breaking change
node_modules/minimist
  mkdirp  0.4.1 - 0.5.1
  Depends on vulnerable versions of minimist
  node_modules/mkdirp
    mocha  1.21.5 - 6.2.2 || 7.0.0-esm1 - 7.1.0
    Depends on vulnerable versions of mkdirp
    node_modules/mocha

5 vulnerabilities (4 low, 1 high)

I have just optimistically pulled all dependencies up to their most recent versions.

'npm test' gave me all ticks both before and after making these changes.

'npm audit' now reports 0 vulnerabilities.

[CLAassistant]

All committers have signed the CLA.

[andyjdavis]

Just checking in on this. There are new versions of some dev dependencies so I've bumped them. Tests still pass, 'npm audit' still reports zero vulnerabilities.

[andyjdavis]

Another round of dependency bumps to get back to 0 vulnerabilities. Tests still pass.