Some commands does not show directory selector, like Rg

[elsonwu]

I have to hack the code right now by changing "grep#runGrep" method to "grep#runGrepRecursive" which works fine, so please consider to update it, thanks.

Origin:

command! -nargs=* -complete=file Rg
	    \ call grep#runGrep('Rg', 'rg', 'set', <f-args>)

Modified:

command! -nargs=* -complete=file Rg
	    \ call grep#runGrepRecursive('Rg', 'rg', 'set', <f-args>)