Cannot use a pretty name for a mermaid subgraph

[travis-leith]

The following mmd works fine on this online editor

sample = "graph TD
subgraph a1[my subgraph]
a --> b
end
a --> c"

sample |> mermaid()

but running it in R does not work. The output is just the input text rendered plainly.

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I am using R 4.2.0, DiagrammeR 1.0.9

[Richard Iannone]

Closing this in favor of #475.