make demo fails due to sed issue in "make demo_content" target

[jasonhildebrand]

In a fresh install on ubuntu 20.04, "make demo" failed with

sed: can't read s/author_email\="mjordan@sfu"\,/author_email="mjordan@sfu", packages=["i7Import", "i8demo_BD", "input_data"],/g: No such file or directory
make[1]: *** [Makefile:374: demo_content] Error 2
make[1]: Leaving directory '/tmp/isle-dc'
make: *** [Makefile:334: demo] Error 2

this turned out to be a OSX vs. GNU sed incompatibility.

I've made a fix and will post a PR shortly.

[jasonhildebrand]

@DonRichards can you please test this? (I don't have access to assign this PR to you.)