Fix warns when using latest Node.js LTS 14.x

$ nuxeo bootstrap
...
(node:62529) Warning: Accessing non-existent property 'cat' of module exports inside circular dependency
(Use `node --trace-warnings ...` to show where the warning was created)
(node:62529) Warning: Accessing non-existent property 'cd' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'chmod' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'cp' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'dirs' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'pushd' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'popd' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'echo' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'tempdir' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'pwd' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'exec' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'ls' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'find' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'grep' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'head' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'ln' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'mkdir' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'rm' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'mv' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'sed' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'set' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'sort' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'tail' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'test' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'to' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'toEnd' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'touch' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'uniq' of module exports inside circular dependency
(node:62529) Warning: Accessing non-existent property 'which' of module exports inside circular dependency

(node:91) Warning: Accessing non-existent property 'cat' of module exports inside circular dependency
    at emitCircularRequireWarning (internal/modules/cjs/loader.js:650:11)
    at Object.get (internal/modules/cjs/loader.js:664:5)
    at Object._register [as register] (/usr/local/lib/node_modules/nuxeo-cli/node_modules/generator-nuxeo/node_modules/shelljs/src/common.js:455:12)
    at Object.<anonymous> (/usr/local/lib/node_modules/nuxeo-cli/node_modules/generator-nuxeo/node_modules/shelljs/src/cat.js:4:8)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)

$ node -v
v14.15.4
$ npm -v
6.14.10