Add support for Node 12, 14 & update dependencies

[StorytellerCZ]

Based on jprichardson#38 I have added extended CI to cover Node 14 and removed CI for EOL Node versions.
Mocha was also updated to the latest version.

This is exactly the same as:
jprichardson#40

Given that node-kexec appears to no longer be maintained we might want to roll our own version for the moment and figure out what to replace this with in the future.

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✅ StorytellerCZ
❌ jrmclaurin
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[i-am-al-x]

@StorytellerCZ can you advise, please, how we can use your "kexec" code to replace the JPRichardson code, for "Node" on linux? I need "node-kexec" to work, so that I can "npm install" and use WebPack with current Node. Is there some branch on GitHub that we can download and manually integrate into the code, to get around the fact that "kexec" has not been updated by JPRichardson? Can we download "meteor/node-kexec" despite the "Contributor License Agreement" problem, or, alternatively, can you get those contributors to indicate their agreement? Given that my concern is with "Node", should I be downloading from the "node-kexec" code-base by JPRichardson, or from the Meteor codebase? What "git" commands do we need to use to get your updates for "kexec", and how do we manually integrate them for Node?

I am an experienced 'C/C++' programmer (though it's been a while; I've mostly been doing javascript this decade).

During "npm install", this happens:

kexec@3.0.0 install /home/.../node_modules/kexec
node-gyp rebuild
. . .
make: *** [Release/obj.target/kexec/src/kexec.o] Error 1