Your graph starts at the 25th of Jan

If you use floor the month you can start with the tick of the month showing

var myExtent = d3.extent(data, function (d) { return; });
myExtent[0] = d3.time.month(myExtent[0]);

And you can also format the value (as in this case 2014 shows instead of Jan)

var xAxis = d3.svg.axis()
    .ticks(d3.time.months, 1)