bug(analytics): add missing Firebase import from analytics index.d.ts

[williamjuan027]

Ran into the following error when using the analytics plugin in a NativeScript Angular project in an Nx workspace.

Property 'analytics' does not exist on type 'Firebase'.ts(2339)

This happens when I try to access the analytics function from the firebase function.

firebase().analytics()

This PR adds the missing Firebase import in the firebase-analytics's index.d.ts file. :)