Test

Update dependency ember-cli-addon-docs to v6 #2755

Job	Run time
Tests	1m 46s
Floating dependencies	1m 33s
ember-try: ember-lts-3.28	1m 31s
ember-try: ember-lts-4.4	1m 42s
ember-try: ember-release	1m 35s
ember-try: ember-beta	1m 58s
ember-try: ember-canary	2m 10s
ember-try: embroider-safe	2m 28s
ember-try: embroider-optimized	1m 34s
ember-try: ember-classic	2m 3s
	18m 20s

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