This replaces nvm in npm-wrapper by harcoding the path the way we do
with node. The main benefit is that this saves a few hundred
milliseconds every time we invoke npm.
NVM takes a specific node version and installs the node package and
a corresponding compatible npm package.
We use it in a somewhat hackish way to install node/npm globally with
a pinned version, since that's how we actually want to consume node in
our development environment.
Other details:
- Travis CI now is configured to use the version of node installed by
provision; the easiest way to do this was to sabotage the existing node
installation.
- jsdom is upgraded to a current version, which both requires recent
node and also is required for the tests to pass with recent node.
This fixes running the node tests on Xenial.
Fixes#1498.
[tweaked by tabbott]
