Will rooting Redmi 4A devices void the warranty in 2017?

No

Xiaomi (just like YU, OnePlus, etc) is one of the brands which doesn't void warranty if you unlock you bootloader, root your device, flash custom recovery, flash custom ROM.

You are free to do any kind of 3rd party development/experiment on your device as long as it's on software side and you are not tampering the hardware.

But in case if device is bricked warranty will get void.

Make sure to flash the latest stable version of stock rom and lock the bootloader to claim the warranty.