fix application crushes with error in AsyncSearch().count() method

[jellex]

I tried using AsyncSearh with next code:

from elasticsearch_dsl import AsyncSearch

search = AsyncSearch(using='my_connection_name', index='my_index_name')
search = search.filter('term', docType='my_docType_name')
result = search.count()

and I get the following error:

  <...>
  File "<..>/elasticsearch_dsl/_async/search.py", line 430, in count
    return await es.count(index=self._index, body=d, **self._params)["count"]
TypeError: 'coroutine' object is not subscriptable

before this bug fix, when calling AsyncSearch().count(), the application crashes with the error TypeError: 'coroutine' object is not subscriptable

[Andrew-Chen-Wang]

You can just do return (await es.count(index=self._index, body=d, **self._params))["count"] to make it in one line.