Fix bug in CollectorRegistry#collectorNames method (#325)

The switch statement was missing breaks for SUMMARY and HISTOGRAM cases.
Due to this bug wrong and duplicate collector names are produced for summaries and histograms.

Author: savulchik

simpleclient/src/main/java/io/prometheus/client/CollectorRegistry.java

@@ -109,10 +109,13 @@ private List<String> collectorNames(Collector m) {
           names.add(family.name + "_count");
           names.add(family.name + "_sum");
           names.add(family.name);
+          break;
         case HISTOGRAM:
           names.add(family.name + "_count");
           names.add(family.name + "_sum");
           names.add(family.name + "_bucket");
+          names.add(family.name);
+          break;
         default:
           names.add(family.name);
       }