Update to Web Chat 4.18.0 with AC schema 1.6

[compulim]

Release of Web Chat can be found at https://github.com/microsoft/BotFramework-WebChat/issues/5239.

[learn-build-service-prod[bot]]

Learn Build status updates of commit fb39997:

:bulb: Validation status: suggestions

File	Status	Preview URL	Details
AdaptiveCards/resources/partners.md	:bulb:Suggestion		Details

AdaptiveCards/resources/partners.md

• Line 23, Column 1: [Suggestion: learn-site-link-broken - See documentation] Link '/cortana/skills/adaptive-cards' points to a learn site page that doesn't exist. Check the path or URL and update the link.

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