fix polar (oh polar)

Author: etpinard

src/plots/polar/micropolar.js

@@ -1071,7 +1071,7 @@ var extendDeepAll = Plotly.Lib.extendDeepAll;
             width: 300,
             height: height + lineHeight,
             xmlns: 'http://www.w3.org/2000/svg',
-            'xmlns:xmlns:xlink': 'http://www.w3.org/1999/xlink',
+            'xmlns:xlink': 'http://www.w3.org/1999/xlink',
             version: '1.1'
         });
         svgEnter.append('g').classed('legend-axis', true);