Gaston gnuplot plots no longer display in Pluto

[mbaz]

Update: Please ignore this question, at least for now. Pluto's built-in package manager was using a different version of Gaston than I thought it was, so I don't fully understand where the issue lies at the moment.

Original question

In Pluto 0.16.x, and (I'm pretty sure) 0.17.1, I was able to display plots using Gaston, a gnuplot front-end for Julia. In 0.17.2, Pluto returns an error message.

By default, Gaston displays plots as PNG files. The plot command returns a value of type Figure. Gaston defines a function Base.show(io::IO, ::MIME"image/png", x::Figure). It also defines a showable function that returns true for image/png MIME types, and false for all others. (It can also be configured to show GIF, PDF, SVG, etcetera..., but by default it does not).

The error returned by Pluto is:

Failed to show value:
MethodError: no method matching show(::IOContext{IOBuffer}, ::Nothing, ::Gaston.Figure)
Closest candidates are:
show(::IO, !Matched::AbstractString, ::Any) at multimedia.jl:111
show(::IO, !Matched::MIME{Symbol("image/gif")}, ::Gaston.Figure) at /home/miguel/.julia/dev/Gaston/src/gaston_aux.jl:246
show(::IO, ::Nothing) at show.jl:967
...
    1. show_richest(::IOContext{IOBuffer}, ::Any)@PlutoRunner.jl:1012
    2. var"#sprint_withreturned#54"(::IOContext{Base.DevNull}, ::Int64, ::typeof(Main.PlutoRunner.sprint_withreturned), ::Function, ::Gaston.Figure)@PlutoRunner.jl:947
    3. format_output_default(::Any, ::Any)@PlutoRunner.jl:842
    4. var"#format_output#42"(::IOContext{Base.DevNull}, ::typeof(Main.PlutoRunner.format_output), ::Any)@PlutoRunner.jl:859
    5. formatted_result_of(::Base.UUID, ::Bool, ::Nothing, ::Module)@PlutoRunner.jl:774
    6. top-level scope@none:1

What does Gaston neet to do in order to get Pluto to properly show a value of type Figure as a PNG image?