Moved node-test-commit-linux-as-shared-lib to ubuntu1804-64

[richardlau]

Quick PSA that I've updated https://ci.nodejs.org/job/node-test-commit-linux-as-shared-lib/ so that it builds on ubuntu1804-64 instead of ubuntu1404-64: https://github.com/nodejs/jenkins-config-test/compare/7dbbbc2af66cb696532dfcf6963497ff09b67d70...97a1bfec56f98e436c6fbf849ff844d8a1f4c92a

It was a fairly quick change while I was editing the job for #2576 and it appears to have fixed a big sea of red due to the compiler on the ubuntu1404-64 machines being too old (gcc/g++ 4.9.4). Given that it has been broken for so long I'm not sure anyone is looking at this job anymore? cc @yhwang (who apparently gets emails on failures) @mhdawson

[mhdawson]

@richardlau + 1 on having moved that.