Update URL for "node_modules checked into source control"

I noticed that
- there is an additional hyphen, and
- www.npmjs.org redirected to docs.npmjs.com
while working on the support ticket #285287

Detect errors

Performance L

Default to NODE_ENV=production during runtime

This was added in 459ebb67 and
mistakenly removed in 043067eb.

test and implementation for performance m dynos

Update README.md

Fix web concurrency tests

changelog format

default to NODE_ENV=production for build and runtime

test and implementation to detect un-downloadable binaries

test and implementation to invalidate cache on runtime signature changes