Fix index intersection example

[jcarlosgarcia]

Looks like this query does not use an index intersection:

db.orders.find( { item: "abc123", qty: { $gt: 15 } } )

This one returns the described stage in the query plan output, showing the use of both indexes:

db.orders.find( { item: "abc123", qty: 15 } )

I think MongoDB does not consider an intersection when using a range in the query

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