[FIX] Prevent incorrect values for `node.elasticsearch.gateway.type`
[FIX] Prevent incorrect values for `node.elasticsearch.gateway.type`

Previously, the elasticsearch.yml file would contain:

    gateway.type: Chef::Node::Attribute

That's because Chef returns a Ruby object as all attribute values, and that object has a `type` method, indeed.

Related: #39

nbudin/cookbook-elasticsearch,zzugg/cookbook-elasticsearch,GemHQ/cookbook-elasticsearch,gouketsu/cookbook-elasticsearch,nbudin/cookbook-elasticsearch,gilt/cookbook-elasticsearch,nbudin/cookbook-elasticsearch,gouketsu/cookbook-elasticsearch,zzugg/cookbook-elasticsearch,vacay/vcy-elasticsearch,spuder/cookbook-elasticsearch,spuder/cookbook-elasticsearch,michaeld/elasticsearch-cookbook,spuder/cookbook-elasticsearch,vacay/vcy-elasticsearch,gilt/cookbook-elasticsearch,vacay/vcy-elasticsearch,zzugg/cookbook-elasticsearch,gilt/cookbook-elasticsearch,paulczar/cookbook-elasticsearch,bavardage/cookbook-elasticsearch,gouketsu/cookbook-elasticsearch