change fillmode from last to previous

pkg/tsdb/postgres/macros.go

@@ -119,8 +119,8 @@ func (m *postgresMacroEngine) evaluateMacro(name string, args []string) (string,
 			switch args[2] {
 			case "NULL":
 				m.query.Model.Set("fillMode", "null")
-			case "last":
-				m.query.Model.Set("fillMode", "last")
+			case "previous":
+				m.query.Model.Set("fillMode", "previous")
 			default:
 				m.query.Model.Set("fillMode", "value")
 				floatVal, err := strconv.ParseFloat(args[2], 64)

pkg/tsdb/postgres/postgres_test.go

@@ -303,12 +303,12 @@ func TestPostgres(t *testing.T) {
 			})
 		})
 
-		Convey("When doing a metric query using timeGroup with last fill enabled", func() {
+		Convey("When doing a metric query using timeGroup with previous fill enabled", func() {
 			query := &tsdb.TsdbQuery{
 				Queries: []*tsdb.Query{
 					{
 						Model: simplejson.NewFromAny(map[string]interface{}{
-							"rawSql": "SELECT $__timeGroup(time, '5m', last), avg(value) as value FROM metric GROUP BY 1 ORDER BY 1",
+							"rawSql": "SELECT $__timeGroup(time, '5m', previous), avg(value) as value FROM metric GROUP BY 1 ORDER BY 1",
 							"format": "time_series",
 						}),
 						RefId: "A",