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');