Update yargs-parser dependency

[jakejarvis]

yargs-parser v18.1.1 fixes a prototype pollution vulnerability:

? ✗ Medium severity vuln found in yargs-parser@16.1.0, introduced via meow@6.0.1
    Description: Prototype Pollution
    Info: https://snyk.io/vuln/SNYK-JS-YARGSPARSER-560381
    From: meow@6.0.1 > yargs-parser@16.1.0

https://app.snyk.io/vuln/SNYK-JS-YARGSPARSER-560381
yargs/yargs-parser#258

Thanks! 😊

[sindresorhus]

I'm merging this to silence the warning for people, but I strongly disagree that this is a vulnerability, and also, Snyk is not a trusted source: https://twitter.com/sindresorhus/status/1123986529498664961