R SIG Debian - Oct 2020 - EXPKEYSIG for CRAN Ubuntu repositories

If you receive the following error when updating and Ubuntu machine that 
utilizes the CRAN based Ubuntu repositories, there is a simple fix.

The following signatures were invalid: EXPKEYSIG 51716619E084DAB9 
Michael Rutter <marutter at gmail.com>

EXPKEYSIG indicates that the key on your system has expired.  I renewed 
my key a month ago, so you just need to update my key using normal 
procedures.  For example:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 
E298A3A825C0D65DFD57CBB651716619E084DAB9

Or any of the other methods mentioned on the CRAN Ubuntu page 
(https://cran.r-project.org/bin/linux/ubuntu/).

If you have any questions, please let me know.
Michael