search a specific folder doesn't work

[jackielii]

per https://github.com/neoclide/coc-lists/issues/58, I should be able to do:

execute 'CocList grep hello' . expand('%:p:h')

To grep for word hello from the folder of current file. However the options produced by grep is:

rg --fixed-strings --color always --max-columns 300 --vimgrep hello /path/to/current/folder -- ./

The problem is https://github.com/neoclide/coc-lists/blob/master/src/grep.ts#L168 always include cwd ./

I propose adding a new option to ignore current folder

[chemzqm]

Added check for --

[jackielii]

Thanks so much for the fast response. Added pr #134