`make container DOCKER=1` fails due to lack of support for stretch by NodeSource

[jrgilman]

Describe the bug
When trying to build the docker container via the make container DOCKER=1 command, the build fails while trying to get node_15.x from nodesource.com due to:

## Your distribution, identified as "stretch", is not currently supported, please contact NodeSource at https://github.com/nodesource/distributions/issues if you think this is incorrect or would like your distribution to be considered for support

To Reproduce
Run: make container DOCKER=1

Expected behavior
Container builds successfully.

Desktop (please complete the following information):

• OS: Ubuntu 16.04.7

Full Error below:

## Confirming "stretch" is supported...

+ curl -sLf -o /dev/null 'https://deb.nodesource.com/node_15.x/dists/stretch/Release'

## Your distribution, identified as "stretch", is not currently supported, please contact NodeSource at https://github.com/nodesource/distributions/issues if you think this is incorrect or would like your distribution to be considered for support

The command '/bin/sh -c curl -sS http://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - &&     echo "deb http://dl.yarnpkg.com/debian/ stable main" |  tee /etc/apt/sources.list.d/yarn.list &&     curl -sL http://deb.nodesource.com/setup_15.x | bash - &&     apt-get install -y nodejs &&     apt-get update &&     apt-get remove cmdtest &&     apt-get install -y yarn' returned a non-zero code: 1
Makefile:113: recipe for target 'ui' failed
make[1]: *** [ui] Error 1
make[1]: Leaving directory '/home/jrgilman/drago'
Makefile:62: recipe for target 'container' failed
make: *** [container] Error 2