Fix build issues related to Node and GLIBC versions

[javagl]

Trying to fix the travis build, which was recently failing with
node: /lib/x86_64-linux-gnu/libc.so.6: version 'GLIBC_2.28' not found (required by node)

Some guesses here:

It probably tries to install the latest (LTS?) version of node, which is now 18, and which needs GLIBC with a version that is higher than the one that is currently installed with the xenial distribution. According to https://docs.travis-ci.com/user/reference/xenial/#javascript-and-nodejs-support , the latest supported Node version in xenial is 12. So I'm giving that a try...

[javagl]

Sooo... the next issue is
error react-scripts@5.0.0: The engine "node" is incompatible with this module. Expected version ">=14.0.0". Got "12.22.12"

Trying 14 now. That doesn't make sense, but ... 🤷‍♂️

[javagl]

Yay. Works.

@weegeekps If you think that this is OK, feel free to hit "merge".

(Yes, Node 14 is not listed as being supported for xenial, but ... I actually don't care too much about that, as long as the build passes. It should be possible to treat the build system as a black box. If anyone disagrees, please give me a summary of all the changes beween GLIBC 2.26, 2.27, 2.28, 2.29, and explain why a newer version was needed here, and why they are not compatible despite the minor version number change)

[weegeekps]

@javagl I think this is fine. Node 14 is going out of support later this year though, so I am going to make it a point to move us to GitHub Actions this or next week and then we can switch back to the latest Node LTS.