vendor: update all dependencies

vendor/go.opencensus.io/metric/metricdata/exemplar.go

@@ -18,6 +18,11 @@ import (
 	"time"
 )
 
+// Exemplars keys.
+const (
+	AttachmentKeySpanContext = "SpanContext"
+)
+
 // Exemplar is an example data point associated with each bucket of a
 // distribution type aggregation.
 //

vendor/go.opencensus.io/metric/metricdata/label.go

@@ -14,6 +14,13 @@
 
 package metricdata
 
+// LabelKey represents key of a label. It has optional
+// description attribute.
+type LabelKey struct {
+	Key         string
+	Description string
+}
+
 // LabelValue represents the value of a label.
 // The zero value represents a missing label value, which may be treated
 // differently to an empty string value by some back ends.

vendor/go.opencensus.io/metric/metricdata/metric.go

@@ -22,11 +22,11 @@ import (
 
 // Descriptor holds metadata about a metric.
 type Descriptor struct {
-	Name        string   // full name of the metric
-	Description string   // human-readable description
-	Unit        Unit     // units for the measure
-	Type        Type     // type of measure
-	LabelKeys   []string // label keys
+	Name        string     // full name of the metric
+	Description string     // human-readable description
+	Unit        Unit       // units for the measure
+	Type        Type       // type of measure
+	LabelKeys   []LabelKey // label keys
 }
 
 // Metric represents a quantity measured against a resource with different