@mohanex correcting uart pins on nexys video

I'm using Vivado 2020.2 and I added the contraints files to it using this git repository but when I started working on my Nexys Video, I had a constant issue with the UART pins not being assigned correctly, furthermore my Serial Monitoring doesn't receive anything. I referred to the [digilent/digilent-xdc](https://github.com/Digilent/digilent-xdc/blob/master/Nexys-Video-Master.xdc) and found out that Rx and Tx pins are inversed so I corrected it.