chore: fix date test when GMT is negative

[edusperoni]

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.
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• All existing tests are passing: https://github.com/NativeScript/nativescript-angular/blob/master/DevelopmentWorkflow.md#running-the-tests
• Tests for the changes are included.

What is the current behavior?

This test fails on negative timezones because 2010-03-17 is interpreted as UTC, while the compared date is created in the local timezone. The formatted date then becomes 2010-03-16 because the object is 2010-03-16T23:00:00 GMT-0100 for example.

https://stackoverflow.com/questions/22959453/javascript-date-using-forward-slashes-vs-hyphens

What is the new behavior?

This test no longer fails

[elena-p]

test