Test

Update dependency ember-cli-addon-docs to v6 #2555

Job	Run time
Tests	1m 18s
Floating dependencies	1m 49s
ember-try: ember-lts-3.28	1m 32s
ember-try: ember-lts-4.4	2m 7s
ember-try: ember-release	1m 29s
ember-try: ember-beta	1m 24s
ember-try: ember-canary	1m 28s
ember-try: embroider-safe	2m 0s
ember-try: embroider-optimized	1m 42s
ember-try: ember-classic	1m 28s
	16m 17s

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