add warning about unversioned cdn urls #1266

Job	Run time
unit_tests (18)	9m 19s
integration_tests / test	5s
lint	3m 18s
unit_tests (20)	9m 10s
unit_tests (22)	9m 20s
lint_markdown_files / lint	1m 10s
fullstack_production_suite / test	4s
unit_tests (24)	9m 4s
Coveralls coverage	-1s
	41m 29s

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