Updated date calculation for "New"

[godanny86]

This is a minor change to the sample ProductTeaser extension and I know its sample code but it confused me when I was looking at the data in Magento.

The isShowBadge() logic calculated the number of days between when the product was created and the current date, but did not take into account Months and years. I.e if the created date was 2019-02-02 and the current date is 2020-02-012 the calculation would return 10 days when its actually 375...

see https://docs.oracle.com/javase/tutorial/datetime/iso/period.html

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Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have signed the Adobe Open Source CLA.
• [ ] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes and the overall coverage did not decrease.
• [ ] All unit tests pass on CircleCi.
• [ ] I ran all tests locally and they pass.