bug#38443: 26.3; nitpicking: in server-process-filter's docstring, -position LINE[:COLUMN] should be -position +LINE[:COLUMN]

[Xu Chunyang]

C-h f server-process-filter says

`-position LINE[:COLUMN]'
  Go to the given line and column number
  in the next file opened.

but I find it doesn't work:

~ $ nc -U $TMPDIR/emacs501/server
-position 10 -file .
-emacs-pid 284
-error Invalid&_&-position&_command&_in&_client&_args
-emacs-pid 284

however, -position +LINE[:COLUMN] works, in other words, + is missed
in the docstring.

~ $ nc -U $TMPDIR/emacs501/server
-position +10 -file .
-emacs-pid 284