For Etherpad 1.7, require node 6.9. Since 1.8, require node 8.9 minimum

A recent issue (#3401) suggests that when using Node <= 4 the application works (edit: as of 1.6.6, it no longer does), but plugins do not get installed. Upgrading to Node 6 solved that specific issue.

Maybe we should decide what is the minumim required Node version, and be clear about that.

installDeps.sh checks for Node >= 0.10:

https://github.com/ether/etherpad-lite/blob/7c971f24aa775f511ad977b8f1ff347ed22f56d0/bin/installDeps.sh#L51

but probably we should reconsider: Node 6 is currently the oldest supported version (going out of support on April 2019).

Using a more recent Node version could probably give us the possibility of modernizing the codebase, too (for example: async/await vs callbacks).

[muxator]

Here’s the support & deprecation plan for the Node runtime for Etherpad 1.7 and 1.8:

Etherpad 1.6.6 does not run on node <= 5 already. Node 6.9 is the first LTS release in the 6 series (EOL April 2019). The current supported LTS release series is 8 (EOL December 2019).

Node version	Etherpad 1.6.6	Etherpad 1.7	Etherpad 1.8
V <= 5	Does not run already	Won’t run. Will print an ERROR and exit	Won’t run. Will print an ERROR and exit
6.9 <= V < 8	Works	Will run. Will print a deprecation WARNING (support to be removed in 1.8). Will use polyfills to shim missing features	Won’t run. Will print an ERROR and exit
V >= 8	Works	Will run	Will run

Work happens in PR #3432.

For Node support status, see: https://github.com/nodejs/Release

[muxator]

A recap on this:

To free resources for development on #3540 (migrate from callback-style to async programming), Etherpad 1.7.5 was released on 2019-01-26. That one will be the last version that runs on Node 6.x.

The first Node LTS version that supports async/await is Node 8, which nicely fits with our plan.

Thus: next version will be 1.8.0, it will get rid of callback hell, and will require Nodejs 8.9 (the first LTS version in branch 8.x).