square brackets are wrongly escaped in code blocks

[xxchan]

// ```rust
// let a = vec![1];
// ```
message Test{}

Will become

/// ```rust
/// let a = vec!\[1\];
/// ```
#[derive(prost_helpers::AnyPB)]
#[derive(Clone, PartialEq, ::prost::Message)]
pub struct Test {
}

[LucioFranco]

Good catch, would be good to fix this and write a test.

[macroexpansion]

Has anyone worked on this yet? I'm happy to help.

[LucioFranco]

@trasua go for it!