Update node engine in package.json

[chicoxyzzy]

We have node 0.11.12 as a lower node version and that's weird. Should we change it to 4.7.0 or maybe even 0.10.48?

[ljharb]

Indeed, it should be as low as is required. However, I'm not sure if npm run build still works on node 0.10 - can someone verify the lowest node version it works on, and we'll adjust the engines field to match?

The original commit that added this, however, indicates why it requires 0.11.12 or later - so I think that the only thing we'd need to do is raise it higher, if in fact it doesn't still work on 0.11.12.

[chicoxyzzy]

npm run build and npm run build:compilers both work on v0.10.48. Would be great if @webbedspace will chime in.

[zloirock]

I don't think that it make any sense. We could just remove it.

[ljharb]

"engines" is important advisory information that, while not required, is still useful to have.