add attribute fillalpha to contourf seriestype for pyplot backend

src/backends/pyplot.jl

@@ -661,6 +661,7 @@ function py_add_series(plt::Plot{PyPlotBackend}, series::Series)
             handle = ax."contourf"(x, y, z, levelargs...;
                 label = series[:label],
                 zorder = series[:series_plotindex] + 0.5,
+                alpha = series[:fillalpha],
                 extrakw...
             )
             push!(handles, handle)
@@ -1098,7 +1099,7 @@ function _before_layout_calcs(plt::Plot{PyPlotBackend})
             end
             pyaxis."label"."set_fontsize"(py_thickness_scale(plt, axis[:guidefontsize]))
             pyaxis."label"."set_family"(axis[:guidefontfamily])
-            
+
             if (RecipesPipeline.is3d(sp))
                 pyaxis."set_rotate_label"(false)
             end