[MIDI] bump: Issue 1: MIDIEvent lacking constructor

I wanted to get the issues list cleared out if possible:  can we reach a
conclusion as to whether we need a MIDIEvent constructor for testing
purposes, or if

var event = new Event("message", {data: [...], receivedTime: t });

suffices, or if we can do something like Marcos suggested:

[Constructor(DOMString type, optional MIDIEventInit eventInitDict)]
interface MIDIMessageEvent : Event {
    readonly    attribute double     receivedTime;
    readonly    attribute Uint8Array data;
};

dictionary MIDIEventInit : EventInit {
    any data;
};

Thoughts?

https://github.com/WebAudio/web-midi-api/issues/1