make ToString() get local date

[dannykentala]

Describe the bug
I am sending the data to the server directly but it is taking by default UTC time so it generates a bug when making a database filter with the date time, maybe is it because when parsing datetime it make it by default UTC ?

toString() { return this.$d.toUTCString() }

Expected behavior
Consider to put by default local datetime

Information

• Day.js Version [e.g. v1.11.13]
• OS: [e.g. iOS]
• Browser [e.g. chrome 62]
• Time zone: [e.g. GMT-07:00 DST (Pacific Daylight Time)]