Update dependency ember-cli-showdown to v8.1.0 #93

Job	Run time
Test Safari	2m 50s
Tests	1m 47s
Node Tests	29s
Docs	1m 16s
Scenario ember-lts-4.8, BS4, Chrome	1m 41s
Scenario ember-lts-4.8, BS5, Chrome	1m 38s
Floating Dependencies	1m 32s
Scenario ember-lts-5.4, BS4, Chrome	1m 24s
Scenario ember-lts-5.4, BS5, Chrome	1m 28s
Scenario ember-release, BS4, Chrome	1m 46s
Scenario ember-release, BS5, Chrome	1m 33s
Scenario ember-beta, BS4, Chrome	1m 40s
Scenario ember-beta, BS5, Chrome	1m 34s
Scenario ember-canary, BS4, Chrome	1m 25s
Scenario ember-canary, BS5, Chrome	1m 36s
Scenario embroider-safe, BS4, Chrome	1m 26s
Scenario embroider-safe, BS5, Chrome	1m 30s
Scenario embroider-optimized, BS4, Chrome	1m 33s
Scenario embroider-optimized, BS5, Chrome	1m 32s
Scenario ember-release, BS4, Firefox	1m 50s
Scenario ember-release, BS5, Firefox	1m 49s
Scenario tracked-toolbox-v1, BS5,	1m 26s
	34m 45s

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