Options provided to plot(..., options=Dict) arent recognized when calling savefig

Hi! The options specified in `P = plot(rand(10, 4), options=Dict(:staticPlot => true))` aren't recognized when I call `savefig(P, "out.html")` and view the resulting HTML file in my browser, as the plot isn't static. (This is the minimal example given in `PlotlyJS.jl/docs/src/syncplots.md`.)

Here's a more full example taken from #326:

```
using PlotlyJS

trace1 = scatter(
x=[0, 1, 2, 3, 4, 5, 6],
y= [1, 9, 4, 7, 5, 2, 4],
mode= "markers",
marker_size = [20, 40, 25, 10, 60, 90, 30]
)

layout = Layout(;
title= "Download Chart as SVG instead of PNG",
showlegend= false
);

config = Dict(
:toImageButtonOptions => Dict(
:format => "svg",
:filename => "custom_image",
:height => 500,
:width => 700,
:scale => 1 # Multiply title/legend/axis/canvas sizes by this factor
)
);
P = plot(trace1,layout;options=config)
savefig(P, "out.html")
```

When I view `out.html` in my browser, the "download image" button still gives a PNG with the default dimensions, not an SVG. The options I specified are not present in the `out.html` source. The problem occurs for me on Julia 1.5.3 with PlotlyJS.jl v0.14.0 or the master HEAD.

Thanks for any help you can provide!