Fix for the latest pyqtgraph 0.10

Author: thocevar

Orange/widgets/utils/classdensity.py

@@ -27,7 +27,7 @@ def class_density_image(min_x, max_x, min_y, max_y, resolution, x_data, y_data,
     y_grid_norm = (np.array(y_grid)-min_y)/(max_y-min_y)
     img = compute_density(x_grid_norm, y_grid_norm,
                           x_data_norm[sample], y_data_norm[sample], np.array(rgb_data)[sample])
-    density_img = ImageItem(img, autoLevels=False)
+    density_img = ImageItem(img.astype(np.uint8), autoLevels=False)
     density_img.setRect(QRectF(min_x-x_sz/2, min_y-y_sz/2,
                                     max_x-min_x+x_sz, max_y-min_y+y_sz))
     density_img.setZValue(-1)