Etherpad 1.8 will deprecate nodejs 8. Etherpad 1.8.3 will require nodejs 10.13.0

[muxator]

In #3424 we started a deprecation plan for nodejs runtimes.

As planned there, Etherpad 1.8 will require nodejs >= 8.9.0, and in the process gets rid of some idioms that only made sense for old nodejs versions (see for example 6d36bb2 and 59a6f2e).

Node.js official release plan reports that node 8.x will be EOLed by december 31th 2019.

This means that:

• Etherpad 1.8 will deprecate node 8.x
• Etherpad 1.8.3 will require node 10.13.0 (the first LTS of the 10.x series)

Edit: let's chose 1.8.3 as cut-off version for getting rid of Nodejs 8. We are pretty sure it will be released after Jan 2020 (by that time node 8 will be EOLed already), and we will still have some minor numbers left for patch releases on Etherpad 1.8.

[muxator]

The next Etherpad version will be 1.8.3 as planned, because we have to respect the deprecation plan, and NodeJS 8 is already out of support.