[DEV-239] Update to node.js version 8

[binoculars]

Purpose

Updates Node.js to a maintained version

Changes

• Add .npmrc to ignore optional dependencies - would use yarn, but ignore-optional flag works not like expected yarnpkg/yarn#2666 is needed before we can use it. livedb's optional dependency, hiredis will not build on newer node.js versions.
• Update Dockerfile to use node.js version 8
  • npm cache clean requires --force flag

Side effects

• May affect the wiki / ShareJS, so we'll need to regression test that
• Assets should be unaffected, but again, something to watch out for

Ticket

https://openscience.atlassian.net/browse/DEV-239

[icereval]

shell'ing scripts directly from the internet is a bit scary. If this script is really worth using rather than the docker hub image, please add a sha256 check directly to the Dockerfile, there should be examples in the docker-library repo.

[binoculars]

Changed it to use that--we can optimize later with multi-stage builds later on once jenkins with modern docker is ready.

[icereval]

@sloria - this will need to be deployed to stage to verify it doesn't break any major functionality so let it bake in a bit, but changes look good (don't expect a break, if anything it more of a miracle our out of date version continued to work 👍 this long)