close code block for issubnormal docstring

[udohjeremiah]

Completes the code block for issubnormal which is currently:

"""
    issubnormal(f) -> Bool

Test whether a floating point number is subnormal.

An IEEE floating point number is [subnormal](https://en.wikipedia.org/wiki/Subnormal_number)
when its exponent bits are zero and its significand is not zero.

# Examples
```jldoctest
julia> floatmin(Float32)
1.1754944f-38

julia> issubnormal(1.0f-37)
false

julia> issubnormal(1.0f-38)
true
"""

Adds "```" before """ at the end

[inkydragon]

LGTM

[giordano]

@mortenpi this isn't the first problem like this that has been fixed recently. Is there a way to automatically detect unclosed fences in docstrings?

[mortenpi]

Bit tricky, because any sequence of characters is valid Markdown. This unclosed code blocks are perfectly valid Markdown.

I suppose, in principle, we could detect paragraph that start with backticks, as that is likely to be an error:

julia> using Markdown

julia> m = md"""
       XYZ

       ```julia
       xyz
       """
  XYZ

  ```julia xyz

julia> m.content
2-element Vector{Any}:
 Markdown.Paragraph(Any["XYZ"])
 Markdown.Paragraph(Any["```julia xyz"])

Actually, that might be reasonably safe, since if you escape the fences, you actually get a slightly different AST:

julia> m = md"""
       XYZ

       \```julia
       xyz

       ```
       """
  XYZ

  ```julia xyz

  ```

julia> m.content
3-element Vector{Any}:
 Markdown.Paragraph(Any["XYZ"])
 Markdown.Paragraph(Any["`", "``julia xyz"])
 Markdown.Paragraph(Any["```"])