Update metrics-v2.graphqls (#43)

Make readMetricsValue return Long value.
diff --git a/metrics-v2.graphqls b/metrics-v2.graphqls
index 0e4fcf2..2009aac 100644
--- a/metrics-v2.graphqls
+++ b/metrics-v2.graphqls
@@ -128,7 +128,7 @@
     typeOfMetrics(name: String!): MetricsType!
 
     # Read metrics single value in the duration of required metrics
-    readMetricsValue(condition: MetricsCondition!, duration: Duration!): Int!
+    readMetricsValue(condition: MetricsCondition!, duration: Duration!): Long!
     # Read time-series values in the duration of required metrics
     readMetricsValues(condition: MetricsCondition!, duration: Duration!): MetricsValues!
     # Read entity list of required metrics and parent entity type.
@@ -141,4 +141,4 @@
     # Read the sampled records
     # TopNCondition#scope is not required.
     readSampledRecords(condition: TopNCondition!, duration: Duration!): [SelectedRecord!]!
-}
\ No newline at end of file
+}