Update spawn-wrap to 1.4.0

[chadxz]

This patch upgrades nyc to spawn-wrap v1.4.0 to allow for setting a custom base path for the spawn-wrap temporary directory. This allows for more customization in the location of files created on disk, to allow for running coverage in environments where write access to the file system is limited.

I'm not actually sure why this change is required. In the nyc package.json file, the version is set to ^1.3.8, which I thought would allow 1.4.0 to install. However, when i set "nyc": "^11.2.1" in my devDependencies, and do npm i && npm ls spawn-wrap from a clean slate with no package-lock.json, I get

└─┬ nyc@11.2.1
  └── spawn-wrap@1.3.8

I'm running node v8.7.0 and npm v5.4.2

[gautaz]

@chadxz Thanks for backing up the spawn-wrap proposal and following up with nyc, it also began with this nyc issue on my side.