Merge branch 'develop' of https://github.com/knsv/mermaid into 1542_take_two

src/diagrams/class/classRenderer-v2.js

@@ -414,6 +414,7 @@ export const draw = function(text, id) {
 
   // Set up an SVG group so that we can translate the final graph.
   const svg = select(`[id="${id}"]`);
+  svg.attr('xmlns:xlink', 'http://www.w3.org/1999/xlink');
 
   // Run the renderer. This is what draws the final graph.
   const element = select('#' + id + ' g');

src/diagrams/class/classRenderer.js

@@ -157,6 +157,7 @@ export const draw = function(text, id) {
 
   // Fetch the default direction, use TD if none was found
   const diagram = select(`[id='${id}']`);
+  diagram.attr('xmlns:xlink', 'http://www.w3.org/1999/xlink');
   insertMarkers(diagram);
 
   // Layout graph, Create a new directed graph
@@ -176,6 +177,7 @@ export const draw = function(text, id) {
 
   const classes = classDb.getClasses();
   const keys = Object.keys(classes);
+
   for (let i = 0; i < keys.length; i++) {
     const classDef = classes[keys[i]];
     const node = svgDraw.drawClass(diagram, classDef, conf);