Specify NODE_ENV in the production build command

[RKushnir]

Hi,
Recently webpacker gem has been updated in a way to make NODE_ENV not fallback to RAILS_ENV(rails/webpacker@e616184).
By default react_on_rails generates this config:

config.build_production_command = 'RAILS_ENV=production bin/webpack'

Before the change in webpacker, this was effectively setting both RAILS_ENV and NODE_ENV to "production", but not anymore. Now NODE_ENV defaults to "development". So if you don't specify it, your production assets will be compiled using dev settings.

---

This change is 

[coveralls]

Coverage remained the same at ?% when pulling 5c92f2d on RKushnir:patch-1 into a1932d9 on shakacode:master.

[justin808]

---

Reviewed 1 of 1 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

---

Comments from Reviewable

[justin808]

@RKushnir Can you please add an entry to the CHANGELOG.md and I'll merge.

---

Review status: all files reviewed at latest revision, all discussions resolved, all commit checks successful.

---

Comments from Reviewable

[RKushnir]

@justin808 Ready.

[justin808]

Thanks @RKushnir!