title: d3 marker is not displayed
body: <p>I have created a force directed graph using <a href="http://bl.ocks.org/d3noob/5141278" rel="nofollow">http://bl.ocks.org/d3noob/5141278</a> example. I have appended the markers to the paths:</p>
  
  <pre><code>var svg = d3.select("#entitiesGraph").append("svg")
  .attr("width", width)
  .attr("height", height);
  
  svg.append("svg:defs").selectAll("marker")
  .data(["end"])
  .enter().append("svg:marker")
  .attr("id", "end")
  .attr("viewBox", "0 -5 10 10")
  .attr("refX", 15)
  .attr("refY", -1.5)
  .attr("markerWidth", 12)
  .attr("markerHeight", 12)
  .attr("orient", "auto")
  .append("svg:path")
  .attr("d", "M0,-5L10,0L0,5");
  
  var path = svg.append("svg:g").selectAll("path")
  .data(force.links())
  .enter().append("svg:path")
  .attr("marker-end", "url(#end)");
  </code></pre>
  
  <p>Everything works fine except the markers - they are not displayed, however in  javascript console I can see that they are appended to the svg container. </p>
  
  <p>Has someone an idea what could be the problem?</p>