Cherry pick v1.7 into master

vendor/gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer/util.go

@@ -1,5 +1,10 @@
 package tracer
 
+import (
+	"strconv"
+	"strings"
+)
+
 // toFloat64 attempts to convert value into a float64. If it succeeds it returns
 // the value and true, otherwise 0 and false.
 func toFloat64(value interface{}) (f float64, ok bool) {
@@ -30,3 +35,16 @@ func toFloat64(value interface{}) (f float64, ok bool) {
 		return 0, false
 	}
 }
+
+// parseUint64 parses a uint64 from either an unsigned 64 bit base-10 string
+// or a signed 64 bit base-10 string representing an unsigned integer
+func parseUint64(str string) (uint64, error) {
+	if strings.HasPrefix(str, "-") {
+		id, err := strconv.ParseInt(str, 10, 64)
+		if err != nil {
+			return 0, err
+		}
+		return uint64(id), nil
+	}
+	return strconv.ParseUint(str, 10, 64)
+}