Counter MetricType is not defined in the rest client

[edmundoa]

On the current master, asking for metrics fails with the following error:

play.api.Application$$anon$1: Execution exception[[IllegalArgumentException: No enum constant org.graylog2.restclient.lib.metrics.Metric.MetricType.COUNTER]]
    at play.api.Application$class.handleError(Application.scala:296) ~[play_2.10-2.3.6.jar:2.3.6]
    at play.api.DefaultApplication.handleError(Application.scala:402) [play_2.10-2.3.6.jar:2.3.6]
    at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$3$$anonfun$applyOrElse$4.apply(PlayDefaultUpstreamHandler.scala:320) [play_2.10-2.3.6.jar:2.3.6]
    at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$3$$anonfun$applyOrElse$4.apply(PlayDefaultUpstreamHandler.scala:320) [play_2.10-2.3.6.jar:2.3.6]
    at scala.Option.map(Option.scala:145) [scala-library.jar:na]
Caused by: java.lang.IllegalArgumentException: No enum constant org.graylog2.restclient.lib.metrics.Metric.MetricType.COUNTER
    at java.lang.Enum.valueOf(Enum.java:236) ~[na:1.7.0_67]
    at org.graylog2.restclient.lib.metrics.Metric$MetricType.valueOf(Metric.java:24) ~[graylog2-rest-client-0.93.0-SNAPSHOT.jar:na]
    at org.graylog2.restclient.models.api.responses.metrics.MetricsListItem.getMetric(MetricsListItem.java:43) ~[graylog2-rest-client-0.93.0-SNAPSHOT.jar:na]
    at org.graylog2.restclient.models.api.responses.metrics.MetricsListResponse.getMetrics(MetricsListResponse.java:36) ~[graylog2-rest-client-0.93.0-SNAPSHOT.jar:na]
    at org.graylog2.restclient.models.Node.getMetrics(Node.java:415) ~[graylog2-rest-client-0.93.0-SNAPSHOT.jar:na]

Looking at the response we get from the server, there are some metrics of type "counter", but they are not defined in the rest client. Here is one of the metrics of that type returned by the server:

    {
      "metric": {
        "count": 0
      },
      "name": "readBlocked",
      "type": "counter",
      "full_name": "org.graylog2.shared.journal.JournalReader.readBlocked"
    }