We were misdetecting the end of the docblock because our `end` regex
could match lines like:
<space><space>"
(ie. a 0 or 1-width space, followed by a non-quote)
Fix that by looking for non-space, non-tab, non-quote instead.
Also, use "\s" for whitespace, so that we deal with tabs properly as
well as spaces.
"
" - Initial release.
-syntax region docvimBlock start='\v^ *""' end='\v\zs\ze^( *$|[^"])'
+syntax region docvimBlock start='\v^\s*""' end='\v^\zs\ze\s*($|[^ \t"])'
syntax region docvimPre start='\v^\s*"\s+\zs```\s*$' end='\v^\s*"\s+```\s*$' containedin=docvimBlock contained keepend
syntax match docvimAnnotation '@command' containedin=docvimBlock contained