D3.js axis gridlines width < 1.0

<!DOCTYPE html>
<meta charset="utf-8">
<style> /* set the CSS */
 
body { font: 12px Arial;}  	/* set the default text for anything occuring in the of the html */
 
	path.line {
	  fill: none;
	  stroke: purple;
	  stroke-width: 1.5;
	}
	  
	path.area {
	  fill: #E2B2B2;
	}
	  
	.axis {
	   shape-rendering: crispEdges;
	}
	   
	.x.axis line {
	   stroke: green;
	   stroke-width: 1.0;
	}
	  
	.x.axis .minor {
	   stroke-opacity: .5;
	   stroke: red;
	   stroke-width: 0.5;
	}
	 
	.x.axis path {
	  display: none;
	}
	   
	.y.axis line, .y.axis path {
	   fill: none;
	   stroke: #17BED5;
	   stroke-width: 1.0;
	}
 
	.y.axis .minor{
	   stroke: #52D12A;
	   stroke-width: 0.5;
	   stroke-opacity: 0.5;
	}
</style>
 
<body>
	<script src="https://d3js.org/d3.v3.min.js"></script>	
 
	<script>
	d3.csv("testData1.csv", function(data) {
		//var data = []
		data.forEach(function(d) {
		  d.date = new Date(d.date);
		  d.close = +d.close; // 1st line data
		  d.open = +d.open; // 2nd line data
		});
		              
		// Find the extent
		var dateExtent = d3.extent(data.map(function(d, i){return d.date;}));
		var trendExtent = d3.extent(data.map(function(d, i){return d.open;}));
 
		var w = 960;
		var h = 400;
		var pad = 73;
 
		var x = d3.time.scale() .domain(dateExtent).range([0,w]);
		var y = d3.scale.linear().domain(trendExtent).range([h,0]);
 
	var	svg = d3.select("body")
	    .append("svg")
		.attr("width", w + pad)
		.attr("height", h + pad);
	    //.append("g").attr("transform", "translate(" + pad + "," + pad + ")");
 
		//var svg =  d3.select("svg").attr("height", h + pad).attr("width", w + pad);
		var vis = svg.append("g").attr("transform", "translate(40,20)");
 
		var lineGenerator = d3.svg.line()
		    .x(function(d) { console.log(1, d);return x(d.date); })
		    .y(function(d) { return y(d.open); })
		    .interpolate("basis");
 
		var xAxis = d3.svg.axis().scale(x).orient("bottom").ticks(4).tickSubdivide(8).tickSize(-h, -h, -50).tickFormat(d3.time.format("%m/%d/%Y"));
 
		var yAxis = d3.svg.axis().scale(y).orient("left").ticks(6).tickSubdivide(5).tickSize(-w, -w, -w);
 
 
		var axisX = vis.append("g").classed("labels x_labels", true)
		    .attr("class", "x axis")
		    .attr("transform", "translate(0,"+h+")")
		    .call(xAxis);
 
		vis.append("g").classed("labels y_labels", true)
		    .attr("class", "y axis")
		    .call(yAxis);
 
 
		vis.append("path")
			.data([data])
			.attr("d", lineGenerator)
		    .attr("class", "line");
 
    });
	</script>
</body>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js