`format_docstrings` break `jldoctest`s

[storopoli]

jldoctests expect an empty line, e.g.:

"""
    fun() = "hello"

\`\`\`jldoctest
julia> fun()
"hello"

\`\`\`
"""
hello() = "hello"

However, upon formatting with format_docstrings = true, JuliaFormatter removes the empty line:

"""
    fun() = "hello"

\`\`\`jldoctest
julia> fun()
"hello"
\`\`\`
"""
hello() = "hello"

This causes the jldoctest to fail.

[domluna]

i'm guessing it's a CommonMark.jl issue but i'll verify.