Microsoft Teams/Azure integration error due to incorrect turnContext method call

I've recently worked on a Microsoft Teams/Azure chatbot integration based on the integration examples in this repo. I received the error "Activity must include non empty 'text' field or at least 1 attachment" in my Azure logs.

This error is due to the incorrect `turnContext` method being called in https://github.com/GoogleCloudPlatform/dialogflow-integrations/blob/master/skype/server.js#L65

Instead of that line reading:

await turnContext.sendActivity(replies);

it should instead read:

await turnContext.sendActivities(replies);