fix: override docs-viewer

Old way of working with ember-keyboard breaks addon-docs. Cleanup
of `docs-viewer` breaks the application. We override the `docs-viewer`
to not use ember-keybard because we don't need this behavior.

tests/dummy/app/components/docs-viewer.js

@@ -0,0 +1,11 @@
+import Component from '@ember/component';
+import layout from 'ember-cli-addon-docs/components/docs-viewer/template';
+import { inject as service } from '@ember/service';
+
+export default Component.extend({
+  layout,
+  docsRoutes: service(),
+  router: service(),
+
+  classNames: 'docs-viewer docs-flex docs-flex1',
+});