How can I stop avoiding poor WiFi automatically?

I have a Motorola G second gen(2014) and I was searching everywhere for a way to stop avoiding poor WiFi automatically by the phone, but I can't find it in my old phone. The option was there in my phone when it was running Kit-Kat 4.4., but I've recently updated my phone to lollipop and I can't find this setting anywhere. Please help.