allow setting the linewidth for contour plots in GR

src/backends/gr.jl

@@ -997,11 +997,13 @@ function gr_display(sp::Subplot{GRBackend}, w, h, viewport_canvas)
             if series[:fillrange] != nothing
                 GR.surface(x, y, z, GR.OPTION_CELL_ARRAY)
             else
+                GR.setlinewidth(series[:linewidth])
                 GR.contour(x, y, h, z, 1000)
             end
 
             # create the colorbar of contour levels
             if cmap
+                gr_set_line(1, :solid, yaxis[:foreground_color_axis])
                 gr_set_viewport_cmap(sp)
                 l = round.(Int32, 1000 + (h - ignorenan_minimum(h)) / (ignorenan_maximum(h) - ignorenan_minimum(h)) * 255)
                 GR.setwindow(xmin, xmax, zmin, zmax)