Fix documentation; "OR" is not Google's default operator

ElasticSearch uses *OR* as the [default operator](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-query-string-query.html) for a `query_string` query if no operator is specified.

The elasticjs documentation says that this is the "same as Google". This is not true; Google uses AND as its default Boolean operator.

For example, see [Google Advanced Search](http://www.google.com/advanced_search) which requires "OR" to be typed for an OR query, but will search for "all these words" (i.e., an AND query) if no operator is used.