Update polar.js

Thanks to the jasmine test, I realized that I changed the wrong line.

Author: Lexachoc

src/plots/polar/polar.js

@@ -560,7 +560,7 @@ proto.updateRadialAxisTitle = function(fullLayout, polarLayout, _angle) {
     var cx = _this.cx;
     var cy = _this.cy;
     var radialLayout = _this.getRadial(polarLayout);
-    var titleClass = _this.id + 'title.text';
+    var titleClass = _this.id + 'title';
 
     var pad = 0;
 
@@ -589,7 +589,7 @@ proto.updateRadialAxisTitle = function(fullLayout, polarLayout, _angle) {
 
     _this.layers['radial-axis-title'] = Titles.draw(gd, titleClass, {
         propContainer: radialLayout,
-        propName: _this.id + '.radialaxis.title',
+        propName: _this.id + '.radialaxis.title.text',
         placeholder: _(gd, 'Click to enter radial axis title'),
         attributes: {
             x: x,