Bumping swagger core version to 1.6.2

[KatseNarniaan]

1.6.2 is the latest in the 1.5 branch of swagger.

I compared the json and yaml files created by the tests with core version 1.5.16 and 1.6.2, and the only thing different was in yaml files:

responses:
        200:
          description: "successful operation"
          schema:
            $ref: "#/definitions/AccountRepresentation"
        404:
          description: "No account found."

became

responses:
        "200":
          description: "successful operation"
          schema:
            $ref: "#/definitions/AccountRepresentation"
        "404":
          description: "No account found."

So the response codes gained quotes with this change.

I was looking into adding the vendor extensions to the swagger-maven-plugin, and those require updating the swagger core to at least 1.5.17, so why not try to upgrade all the way.