Adjust markdown code fences filetype regex

This highlighter (line 50 of markdown.kak) looks for the filetype
specified by the author at the top of the code fence, e.g.

``` python
print("hello")
```

and highlights the code within using Kakoune's relevant highlighter --
in this case Python.

Some flavours of markdown use curly braces and other characters in the
first line such as the following:

``` {=python}
print("hello")
```

Previously Kakoune recognised `{=python}` but not `{.python}`.  The latter
is Pandoc's flavour of markdown.  This patch adjusts the regex patterns
to recognise the dot notation as well.

0 files changed, 0 insertions, 0 deletions