fix(markdown): Don't include next heading in previous heading's range

Somehow marksman also does this?

As for treesitter (norg) it may be because treesitter includes the
newline and the next line indent until the next heading, so the line of
the next heading is included in the range of the previous heading. We
manually -1 on the range end line to fix it.

CHANGELOG.md

@@ -76,6 +76,7 @@
 - A built-in provider for `norg` files that displays headings in the outline is now
   provided. This requires `norg` parser to be installed for treesitter
 - Outline.nvim now supports per-tabpage outlines
+  ([#37](https://github.com/hedyhli/outline.nvim/issues/37))
 
 ### Fixes
 
@@ -99,6 +100,10 @@
   ([#19](https://github.com/hedyhli/outline.nvim/issues/19))
 - Fixed display of JSX Fragments due to recent update from `javascript` TS
   parser
+- Markdown parser included the next heading when setting the end range for
+  previous heading. So when cursor was on the next heading, the previous heading
+  would also be highlighted in the outline. This is now fixed, but marksman LSP
+  would still do this. A "fix" is to add marksman into lsp client blacklist.
 
 ### Performance