Upgrade common vendoring

Godeps/Godeps.json

@@ -60,11 +60,11 @@
 		},
 		{
 			"ImportPath": "github.com/prometheus/common/expfmt",
-			"Rev": "2502df85be1b9482ed669faa6b7cfe7f850eb08e"
+			"Rev": "675b18b12eb9d452d0377f1688d62e724f15b882"
 		},
 		{
 			"ImportPath": "github.com/prometheus/common/model",
-			"Rev": "2502df85be1b9482ed669faa6b7cfe7f850eb08e"
+			"Rev": "675b18b12eb9d452d0377f1688d62e724f15b882"
 		},
 		{
 			"ImportPath": "github.com/prometheus/client_model/go",

Godeps/_workspace/src/github.com/prometheus/common/model/value.go

@@ -243,8 +243,8 @@ func (e ValueType) String() string {
 
 // Scalar is a scalar value evaluated at the set timestamp.
 type Scalar struct {
-	Value     SampleValue `json:"value"`
-	Timestamp Time        `json:"timestamp"`
+	Value     SampleValue
+	Timestamp Time
 }
 
 func (s *Scalar) String() string {
@@ -253,8 +253,8 @@ func (s *Scalar) String() string {
 
 // String is a string value evaluated at the set timestamp.
 type String struct {
-	Value     string `json:"value"`
-	Timestamp Time   `json:"timestamp"`
+	Value     string
+	Timestamp Time
 }
 
 func (s *String) String() string {