add support for new array operators in mongodb 3.6 for minimongo

[turbobuilt]

Mongodb 3.6 lets you update a specific property of all objects in an array with the following syntax. Requesting support for it in minimongo

Items.update({ _id: item._id }, {                                                                                                           
    $set: {                                                                                                            
        "child.$[].value": newValue                                                       
    }                                                                                                          
}

[crapthings]

https://github.com/meteor/meteor-feature-requests/issues/268