improvement on issue55: TZ is not recognized as a command or cmdlet in Powershell context on Windows system

[SafeWinter]

Issue description: When running command npm run test on my computer (Win10), the testing process aborted due to the unrecognized 'TZ' argument (see the attachment file)

Solution: Add cross-env as a dev-dependency would solve this incompatibility issue. After its installation, the original 'test' script need to be updated like this:

{
    // ...
    "scripts": {
        "test": "cross-env TZ=America/Los_Angeles mocha 'test/**/*-test.js' && eslint src test",
    // ...
}

Then rerun the test, everything get back to normal.

[SafeWinter]

Adding cross-env by npm i cross-env -D and rerunning npm run test, all tests passed as expected:

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Original issue: see #55