fix some types

[franmomu]

I was trying to use strict types and some issues appeared:

• active_shards_percent_as_number returns a float according to https://www.elastic.co/guide/en/elasticsearch/reference/current/cluster-health.html#cluster-health-api-response-body
• Elastica\Multi\Search:: addSearch() $key parameter could be an int if no key is specified when calling addSearches or setSearches.