Fix incorrect field name in express authentication example

[kyu08]

Thank you for maintaining Genkit always!
Genkit provides us high productivity and flexibility. 👍

Problem I encountered

I got a following error when I tried this example

• Object literal may only specify known properties, and 'context' does not exist in type '{ contextProvider?: ContextProvider<ActionContext, ZodObject<{ input: ZodString; }, "strip", ZodTypeAny, { input: string; }, { input: string; }>>; }'. 

Solution

As of @genkit-ai/[email protected], it works if I specify contextProvider instead of context.

So I replaced context with contextProvider.

Testing

I have confirmed it looks fine as below locally by running pnpm dev.