Node: npm bump, devel killed, npm update change.

Okay, this is part 1 of what will likely become a host of wider changes I propose on Node to tackle the issues discussed in [#31777](https://github.com/Homebrew/homebrew/issues/31777).

Part 1: I’ve killed the devel build. It hasn’t been updated since May, and Node haven’t expressed any sort of haste in issuing even a new minor bump to the devel build that fixes the rather large [OpenSSL vulnerabilities](https://github.com/joyent/node/tree/v0.11.13-release/deps/openssl/openssl) in 0.11.13. 

At this point, my feeling is that it’s dangerously irresponsible to leave the devel build present given those
vulnerabilities, and I’d like to see us scrap it until we see some movement on patching those issues. This issue is open with Node [here](https://github.com/joyent/node/issues/8000) but remains largely ignored and dormant.

Second change: Bumps the npm version that we ship back to the latest stable release. A minor thing, but an early step towards fixing some of the bigger npm problems.

Third change: Changes the way we handle npm updates post-install to specifically target the latest stable release. Our current ``` npm update npm -g ``` has been habitually dumping people onto the alpha & beta builds for npm, and this solution (according to the npm team) should solve that problem permanently. Having done local testing with this, It does indeed seem to do the job.

These are largely minor fixes to patch things over in a stable, solid fashion till I can work out ways to avoid the Node issues we’ve been encountering so rampantly lately.
This is intentionally not `--global` as we want it to just install into the test directory and then be cleaned up afterwards.