docs: Correct uv.spawn options.args docs about the first argument

[squeek502]

This was left over from the libuv docs, but the luv bindings handle this differently and options.args should only include the command arguments, not the command name itself.

See #673 (comment)

Example from our tests:

luv/tests/test-process.lua

Lines 14 to 31 in dcd1a1c

	if isWindows then
	cmd = "cmd.exe"
	args = {"/c", "echo "..input}
	expectedOutput = input .. "\r\n"
	else
	cmd = "echo"
	args = {input}
	expectedOutput = input .. "\n"
	end
	local handle, pid
	handle, pid = uv.spawn(cmd, {
	args = args,
	stdio = {nil, stdout},
	}, expect(function (code, signal)
	p("exit", {code=code, signal=signal})
	uv.close(handle)
	end))

[zhaozg]

provided via path by luv, this is slightly different with libuv.

[squeek502]

I think it's okay to leave this out because these are the luv docs, so it should be implied.