Fix chartJS generate image issue #786

Author: girishpanchal30

js/render-chartjs.js

@@ -118,7 +118,15 @@
                 labels: labels,
                 datasets: datasets
             },
-            options: settings
+            options: settings,
+            plugins: [{
+                afterRender: function () {
+                    var canvas = $( 'canvas' )[0];
+                    if ( $( '#chart-img' ).length ) {
+                        $( '#chart-img' ).val( canvas.toDataURL() );
+                    }
+                },
+            }],
         });
 
         // this line needs to be included twice. This is not an error.