[now-build-utils][now-static-build][now-node] Add node 12.x

[styfle]

This PR adds support for Node 12 when the user defines engines in their package.json

[codecov-io]

Codecov Report

Merging #3330 into master will increase coverage by 2.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3330      +/-   ##
==========================================
+ Coverage   11.67%   13.76%   +2.08%     
==========================================
  Files         267      267              
  Lines       10182    10446     +264     
  Branches     1357     1262      -95     
==========================================
+ Hits         1189     1438     +249     
- Misses       8896     8937      +41     
+ Partials       97       71      -26

Impacted Files	Coverage Δ
src/util/metrics.ts	68.18% <0%> (-2.41%)	⬇️
src/util/dev/builder-cache.ts	84.66% <0%> (+2.64%)	⬆️
src/util/dev/router.ts	80.76% <0%> (+3.49%)	⬆️
src/util/get-files.ts	91.08% <0%> (+4.26%)	⬆️
src/util/projects/get-project-by-id-or-name.ts	26.66% <0%> (+4.44%)	⬆️
src/util/dev/builder.ts	70.49% <0%> (+5.1%)	⬆️
src/util/dev/yarn-installer.ts	89.09% <0%> (+5.36%)	⬆️
src/util/dev/server.ts	64.61% <0%> (+5.77%)	⬆️
src/util/prefer-v2-deployment.ts	60.46% <0%> (+5.91%)	⬆️
src/util/output/create-output.ts	65% <0%> (+7.42%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d1b59c3...af4554d. Read the comment docs.