scatterPlot.js : change default_margin values

See #2420

browser/js/scatterPlot.js

@@ -49,7 +49,7 @@ function ScatterPlot(id, model, database) {
     this.gridSizeH = 1; //grid height
 
     //Margins (css style : top/right/bottom/left)
-    this.default_margin = [75,10,25,120];
+    this.default_margin = [40,10,20,100];
     this.graph_margin = [25,25,25,25];
     this.margin = this.default_margin;