Add json-iterator dep, remove ugorji dep

vendor/github.com/json-iterator/go/feature_json_number.go

@@ -0,0 +1,15 @@
+package jsoniter
+
+import "encoding/json"
+
+type Number string
+
+func CastJsonNumber(val interface{}) (string, bool) {
+	switch typedVal := val.(type) {
+	case json.Number:
+		return string(typedVal), true
+	case Number:
+		return string(typedVal), true
+	}
+	return "", false
+}