Need to import GraphiQl namespace since GraphiQL 1.2.0

[Cito]

Adding the app.UseGraphiQl() middleware does not seem to work in GraphiQL 1.2.0 unless you add using GraphiQl to Startup.cs. In version 1.1.0 it this does not seem to be necessary. This should be explicitly mentioned in the README and also added to the graphiql.example, if it's not considered a regression.

[josephwoodward]

@Cito Thanks for bringing this to my attention.

Do you not get a compilation error if the namespace isn't imported?