Node 12

[jhuleatt]

Summary

Like #437 moved this repo from Node 7 to Node 8, this PR moves us from Node 8 to Node 12. We're doing this because (1) Node 8 is end-of-life, and (2) Cloud Functions support for the Node 8 runtime was deprecated on June 5, 2020.

Note that, after this update, samples in this repository will require a billing account to deploy. Per the pricing guide:

Node.js 10 or later runtimes require the Pay as you go (Blaze) plan

Status

• Update engines field to 12 in package.json
• Update firebase-functions and firebase-admin version in package.json
• Update firebase version in package.json and *.html files
• Update README.md with a note about Node 12 and Blaze plan required
• Manually test a subset of samples to make sure they still build, deploy, and run:
  • Quickstarts:
    • HTTPS trigger quickstart: Time Server
    • Hosting triggered HTTPS function quickstart: Big Ben
    • Uppercaser for Realtime Database
    • Uppercaser for Cloud Firestore
    • Cloud Storage trigger quickstart: Thumbnail generator
    • Auth trigger quickstart: Welcome Email
    • PubSub trigger quickstart: Hello World
    • Crashlytics trigger quickstart: Crashlytics Email Notifier
    • Test Lab trigger quickstart: Log when a matrix completes
  • Other samples:
    • Write Cloud Functions using TypeScript (to check TS compilation)
    • Isomorphic React App (to check that the client SDK updates don't break it)
    • Moderate offensive images (to check for Cloud Vision API incompatibility)

⚠️ Help wanted: Anyone that has some time to pull this branch, test one of the samples, and comment in this PR whether it works or whether the Node 12 migration broke it, would be a huge help!

[samtstern]

Be careful with this one, import styles changed