Add whitespaces trimming at duration unmarshalling (#19)

duration.go

@@ -25,6 +25,7 @@ func (dur Duration) MarshalText() ([]byte, error) {
 // UnmarshalText implements the encoding.TextUnmarshaler interface.
 func (dur *Duration) UnmarshalText(data []byte) (err error) {
 	s := string(data)
+	s = strings.TrimSpace(s)
 	if s == "" || strings.ToLower(s) == "undefined" {
 		*dur = 0
 		return nil

duration_test.go

@@ -40,6 +40,10 @@ func TestDurationUnmarshal(t *testing.T) {
 		assert.Equal(t, Duration(2*time.Second), d)
 	}
 	d = 0
+	if assert.NoError(t, d.UnmarshalText([]byte(" 00:00:02 "))) {
+		assert.Equal(t, Duration(2*time.Second), d)
+	}
+	d = 0
 	if assert.NoError(t, d.UnmarshalText([]byte("00:02:00"))) {
 		assert.Equal(t, Duration(2*time.Minute), d)
 	}