Upgrade node-client-api to use node 14

[anu3990]

Currently, the node-client-api uses node version -10. We are introducing compatibility with node version -14 to make use of new node features.

[ehennum]

Here's the Node.js timeline:

https://nodejs.org/en/about/releases/

[georgeajit]

Verified on 06/22/21 : https://jenkins.marklogic.com/view/Node%20API/job/NodeAPIUnitTests_develop_b10_0/3467/console

+ which node
/bin/node
+ node --version
v14.16.1
+ node etc/test-setup.js -u admin:admin
checking for REST users