fix: fix unit tests with node v12.11.0

[Fatme]

Unit tests cannot be executed with node v12.11.0 due to the changes in util.format. If you have the following code:

const obj = { obj: 1 }
const formattedValue = util.format("%s", obj);
console.log(formattedValue);

The output with node v10.13.0 is:

[object Object]

The output with node v12.11.0 is:

{ obj: 1 }

However, the string interpolation is not changed i.e the following code:

console.log(`${obj}`)

will result in [object Object] no matter if it is executed with node v12.11.0 or earlier.

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].