Update CUDA from 9.1 to 10.1 on Ubuntu 18.04

Newer software is being compiled against CUDA 10.2. But some software we use may require specific versions. In this case, we require CUDA 10.1, but we already have CUDA 9.1 installed. Lets walk through how to get your system upgraded from CUDA 9.1 to 10.1 on Ubuntu 18.04.