fix(vdatepicker): fix min date

[YipingRuan]

fix #9039

Description

Fix min date compare logic (Inclusive)

Motivation and Context

#9039

How Has This Been Tested?

Visually and added unit test

Markup:

<template>
  <v-container>
    {{ min }}
    <v-date-picker :min="min"></v-date-picker>
  </v-container>
</template>

<script>
export default {
  data: () => ({
    min: '2019-09-28T15:55:56.441Z'
  })
}
</script>

Types of changes

• 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 not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and breaking changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)
• I've added new examples to the kitchen (applies to new features and breaking changes in core library)

[dsseng]

Looks good, but please add a unit test corresponding to your changes

[dsseng]

Looks good