Dependency installation doesn't respect NODE_ENV

[RealOrangeOne]

Perhaps related to #522

I've just hit an interesting bug with how npm ci is currently being used. The current setup ignores NODE_ENV=production, and explicitly uses NPM_CONFIG_PRODUCTION to drive whether devDependencies should be installed, which doesn't match how npm ci works.

I think the fix for this is to remove the explicit handling of --production during install, so it's handled explicitly by npm, and how it wants to install dependencies based on arguments. This makes sure it matches how it works in non-heroku environments, such as CI.

heroku-buildpack-nodejs/lib/dependencies.sh

Line 182 in 11caac6

monitor "npm-install" npm install --production="$production" --unsafe-perm --userconfig "$build_dir/.npmrc" 2>&1

[danielleadams]

Thanks @RealOrangeOne. I'll take a look at this.