date utils: isSameDate() returns erroneous results in certain scenarios

[rstoenescu]

Test-case:

<template>
    <q-datetime
      v-model="model"
      type="date"
      no-clear
      modal
      format="DD/MM/YY"
      min="Mon Feb 19 2018 00:00:00 GMT+0200 (EET)"
      :max="now"
    />
</template>

<script>
export default {
  data () {
    return {
      model: null,
      now: new Date(2018, 3, 20)
    }
  }
}
</script>

Steps to reproduce:

1. Click on datetime component
2. Click on day 1. --> view is messed up, looking as if showing february instead of march

Why?
Underlying code uses date utils isSameDate() which uses UTC time instead of local time.