shim: refactor nodejs shim to work on node8 or node10

[skabbes]

No breaking changes to any code, you can simply specify:

"lambda": {
  "runtime": "nodejs10.x"
}

to select the nodejs 10.x runtime on AWS. The node 8 runtime will continue to work, as the shim is compatible with both versions of node.

I have run this against our company's internal website with no issue (node 8), and will run on node10 this afternoon to burn that in too.

[skabbes]

Several hours on node8, and coming up on 24 hours on a few sites that gets probably 1QPS in aggregate for node10.

Still not sure that "runtime" is the best way to expose whether you want node8 or node10. It is going to be forever confusing due to the "proxy runs on X platform, your code runs Y".

[skabbes]

Over 1 week of testing "in production" on a node.js server running node10. And several "static" sites as well, no problem - all running smoothly.

I used to embed node10 directly in the lambda package, and saved so much extra space not having to do that anymore. Now, I have so much more room for left-pad and similar node_modules!

[tj]

Whoop! I'll check this out again when I'm back from NYC next week!

[tj]

merged! thanks man!

[loganpowell]

Thank you @skabbes !