Use `npm ci` instead of `npm i` if it's supported

[frontsideair]

npm ci is way faster than npm install so we should use it when it's available. Requirements:

• npm version is >5.7.0
• a package-lock.json or npm-shrinkwrap.json exists (we already check for package-lock.json)

Things to do:

• Check npm version
• Add checking for npm-shrinkwrap.json #19
• Add a flag for using npm install instead of npm ci
• Can we fallback to npm install if npm ci fails?

[frontsideair]

I think it's supposed to work when there's no node_modules present like in a CI environment. Closing.