Bug when serializing resources with HalEmbeddedBuilder 

I encountered a bug in HalEmbeddedBuilder. Adding more than 2 values with the same reltype to an embedded collection will result in somthing like this:

```
  "_embedded" : {
    "listItem" : {
      "label" : "lorem",
      "_links" : {
        "self" : {
          "href" : "http://localhost:3000/rest/lists/lorem"
        }
      }
    },
    "listItems" : [ {
      "label" : "ipsum",
      "_links" : {
        "self" : {
          "href" : "http://localhost:3000/rest/lists/ipsum"
        }
      }
    }, {
      "label" : "dolor",
      "_links" : {
        "self" : {
          "href" : "http://localhost:3000/rest/lists/dolor"
        }
      }
    } ]
  }

```

A fourth item would be merged with the single `listItem` and then replace the collection and so on...