You can do it one of two ways; if you wanted a label of each calendar then you can just duplicate the module with the alternating title and calendar link.
EG:

			module: "calendar",
			header: "US Holidays",
			position: "top_left",
			config: {
				calendars: [
					{
						symbol: "calendar-check",
						url: "webcal://www.calendarlabs.com/templates/ical/US-Holidays.ics"
					}
				]
			}
		},
		{
			module: "calendar",
			header: "Another Calendar",
			position: "top_left",
			config: {
				calendars: [
					{
						symbol: "calendar-check",
						url: "webcal://www.calendarlabs.com/templates/ical/Another-calendar-link.ics"
					}
				]
			}
		},

The other option is to place the links in the one calendar.
EG:

	{
			module: "calendar",
			header: "US Holidays",
			position: "top_left",
			config: {
				calendars: [
					{
						symbol: "calendar-check",
						url: "webcal://www.calendarlabs.com/templates/ical/US-Holidays.ics"
					},
                                       {
                                       						symbol: "calendar-check",
                                       						url: "webcal://www.calendarlabs.com/templates/ical/AnotherCalendar.ics"
                                      },
                                     {
                                     						symbol: "calendar-check",
                                     						url: "webcal://www.calendarlabs.com/templates/ical/AndAThirdOneIfYouWant.ics"
                                     	}
				]
			}
		}