Test

Update dependency ember-cli-addon-docs to v6 #2706

Job	Run time
Tests	1m 54s
Floating dependencies	1m 19s
ember-try: ember-lts-3.28	1m 32s
ember-try: ember-lts-4.4	1m 40s
ember-try: ember-release	1m 34s
ember-try: ember-beta	1m 42s
ember-try: ember-canary	1m 30s
ember-try: embroider-safe	1m 59s
ember-try: embroider-optimized	1m 39s
ember-try: ember-classic	1m 31s
	16m 20s

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