Add tick size to burndown text serialization

Signed-off-by: Robert Lin <robertlin1@gmail.com>

leaves/burndown.go

@@ -974,6 +974,7 @@ func addBurndownMatrix(matrix DenseHistory, granularity, sampling int, accPerTic
 func (analyser *BurndownAnalysis) serializeText(result *BurndownResult, writer io.Writer) {
 	fmt.Fprintln(writer, "  granularity:", result.granularity)
 	fmt.Fprintln(writer, "  sampling:", result.sampling)
+	fmt.Fprintln(writer, "  tick_size:", result.TickSize)
 	yaml.PrintMatrix(writer, result.GlobalHistory, 2, "project", true)
 	if len(result.FileHistories) > 0 {
 		fmt.Fprintln(writer, "  files:")

leaves/burndown_test.go

@@ -620,6 +620,7 @@ func TestBurndownSerialize(t *testing.T) {
 	assert.Nil(t, bd.Serialize(out, false, buffer))
 	assert.Equal(t, buffer.String(), `  granularity: 30
   sampling: 30
+  tick_size: 24h0m0s
   "project": |-
     1145    0
      464  369
@@ -708,6 +709,7 @@ func TestBurndownSerializeAuthorMissing(t *testing.T) {
 	assert.Nil(t, bd.Serialize(out, false, buffer))
 	assert.Equal(t, buffer.String(), `  granularity: 30
   sampling: 30
+  tick_size: 24h0m0s
   "project": |-
     1145    0
      464  369