add warning about unversioned cdn urls #1267

Job	Run time
lint	3m 44s
fullstack_production_suite / test	6s
unit_tests (18)	8m 11s
unit_tests (20)	7m 58s
unit_tests (22)	8m 13s
unit_tests (24)	8m 12s
lint_markdown_files / lint	1m 5s
integration_tests / test	5s
Coveralls coverage	0s
	37m 34s

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