vendor: update buildkit to master@31c870e82a48

Signed-off-by: Justin Chadwell <me@jedevc.com>

vendor/github.com/aws/smithy-go/encoding/json/encoder.go

@@ -0,0 +1,30 @@
+package json
+
+import (
+	"bytes"
+)
+
+// Encoder is JSON encoder that supports construction of JSON values
+// using methods.
+type Encoder struct {
+	w *bytes.Buffer
+	Value
+}
+
+// NewEncoder returns a new JSON encoder
+func NewEncoder() *Encoder {
+	writer := bytes.NewBuffer(nil)
+	scratch := make([]byte, 64)
+
+	return &Encoder{w: writer, Value: newValue(writer, &scratch)}
+}
+
+// String returns the String output of the JSON encoder
+func (e Encoder) String() string {
+	return e.w.String()
+}
+
+// Bytes returns the []byte slice of the JSON encoder
+func (e Encoder) Bytes() []byte {
+	return e.w.Bytes()
+}