runtime: update vimCommand syntax pattern (#6976)

Update a flawed match pattern for the vimCommand syntax group. To see
the effect of this fix, open a vimscript buffer,

  nvim -u NONE foo.vim

configure a couple highlight groups,

  :hi! vimIsCommand ctermfg=Green
  :hi! vimCommand ctermfg=Red
  :syntax enable

and add the following lines to the buffer:

  let foo=xFoo
  let bar=zBar

You'll notice the "z" in zBar is Red, while xFoo and the rest of Bar are green. This will
be the case as long as the word following `=` starts with the letter "z". This has already
been fixed upstream by adding a "\>" word boundary to the match pattern:

  https://github.com/vim/vim/issues/124
  https://github.com/vim/vim/commit/e2719096250a19ecdd9a35d13702879f163d2a50#diff-86da060e2153c8ce5dc317a7b4b5a29dR27

This particular match pattern was also mentioned in issue #5491, but in reference to a bug
that was related to the generated part of syntax/vim.vim, whereas this bug lives in the
non-generated part of the file.

0 files changed, 0 insertions, 0 deletions