FiltersAggregation generates invalid array

[niels-nijens]

The FiltersAggregation adds filters inside an array with the type as key. Though, this generates the following array for a TermQuery with the 'term'-key twice in the stack:

array(
    'filtername' => array(
        'term' => array(
            'term' => array(
                'fieldname' => 'fieldvalue'
            )
        )
    )
)

This filter will throw an exception when sending it with a query to an Elasticsearch server.

I can supply a PR to fix this issue if you want.

[saimaz]

Sure, you are welcome to open a PR.