build(npm): mandate Node.js engine version

This change mandates a particular version of Node.js when running
`npm install`. When using a version of Node.js that does not meet these
expectations, a warning will be emitted to the user to let them know
that they are using an unsupported version of Node.js

Change-Id: I3f9bcf8be483a80b5882d65b034c6655013df19f
Signed-off-by: Chris Kay <chris.kay@arm.com>