Comment 9 for bug 1563090

@rajasingh012 Fist, you need to add the Mono Project GPG signing key and the package repository to your system, as seen here: http://www.mono-project.com/docs/getting-started/install/linux/#debian-ubuntu-and-derivatives

Then, you have to pin the package to not install from ubuntu repo, which provides a higher version. Edit file /etc/apt/preferences and put the following:

Package: monodevelop
Pin: origin archive.ubuntu.com
Pin-Priority: -1

Run apt-get update

Finally, you can downgrade with:

# sudo apt install monodevelop=5.10.0.871-0xamarin2