DOT format exporter can't treat strings that have spaces

[Paalon]

For example, the following gives ill-formed DOT format file.

using Graphs
using MetaGraphsNext

complicated = MetaGraph(
    DiGraph();
    label_type=String,
    vertex_data_type=Dict{Symbol, String},
    edge_data_type=Dict{Symbol, String},
    graph_data=(tagged=true,)
);

complicated["lnsgkgsnl/1r5b1/ppppppppp/9/9/9/PPPPPPPPP/1B5R1/LNSGKGSNL b -"] = Dict(:label => "初期局面")

complicated["lnsgkgsnl/1r5b1/ppppppppp/9/9/7P1/PPPPPPP1P/1B5R1/LNSGKGSNL w -"] = Dict(:label => "☗２６歩");

complicated["lnsgkgsnl/1r5b1/ppppppppp/9/9/9/PPPPPPPPP/1B5R1/LNSGKGSNL b -", "lnsgkgsnl/1r5b1/ppppppppp/9/9/7P1/PPPPPPP1P/1B5R1/LNSGKGSNL w -"] = Dict(:label => "2g2f");

complicated_str = mktemp() do file, io
    savegraph(file, complicated, DOTFormat())
    read(file, String)
end

print(complicated_str)

digraph G {
    tagged = true
    lnsgkgsnl/1r5b1/ppppppppp/9/9/9/PPPPPPPPP/1B5R1/LNSGKGSNL b - [label = "初期局面"]
    lnsgkgsnl/1r5b1/ppppppppp/9/9/7P1/PPPPPPP1P/1B5R1/LNSGKGSNL w - [label = "☗２６歩"]
    lnsgkgsnl/1r5b1/ppppppppp/9/9/9/PPPPPPPPP/1B5R1/LNSGKGSNL b - -> lnsgkgsnl/1r5b1/ppppppppp/9/9/7P1/PPPPPPP1P/1B5R1/LNSGKGSNL w - [label = "2g2f"]
}

because it requires quotations "

digraph G {
    tagged = true
    "lnsgkgsnl/1r5b1/ppppppppp/9/9/9/PPPPPPPPP/1B5R1/LNSGKGSNL b -" [label = "初期局面"]
    "lnsgkgsnl/1r5b1/ppppppppp/9/9/7P1/PPPPPPP1P/1B5R1/LNSGKGSNL w -" [label = "☗２６歩"]
    "lnsgkgsnl/1r5b1/ppppppppp/9/9/9/PPPPPPPPP/1B5R1/LNSGKGSNL b -" -> "lnsgkgsnl/1r5b1/ppppppppp/9/9/7P1/PPPPPPP1P/1B5R1/LNSGKGSNL w -" [label = "2g2f"]
}