Expose appInsights.setAuthenticatedUserContext

[darshanrampatel]

Currently fails with:

TypeError: appInsights.setAuthenticatedUserContext is not a function

This should be a valid as per https://azure.microsoft.com/en-gb/documentation/articles/app-insights-web-track-usage/#authenticated-users

I believe this will be fixed by pull request #5 but I'm not sure.

[hurricaneMitch]

I am also hitting this issue also

[shivbijlani]

I see a few of these every now and then:
setAuthenticatedUserContext is not a function

These errors are reported - by appinsights :-)