Fix a bug where months are padded with 0

Author: Mahmood Ali

cronexpr_parse.go

@@ -78,15 +78,15 @@ var (
 		"2090": 2090, "2091": 2091, "2092": 2092, "2093": 2093, "2094": 2094, "2095": 2095, "2096": 2096, "2097": 2097, "2098": 2098, "2099": 2099,
 	}
 	monthTokens = map[string]int{
-		`1`: 1, `jan`: 1, `january`: 1,
-		`2`: 2, `feb`: 2, `february`: 2,
-		`3`: 3, `mar`: 3, `march`: 3,
-		`4`: 4, `apr`: 4, `april`: 4,
-		`5`: 5, `may`: 5,
-		`6`: 6, `jun`: 6, `june`: 6,
-		`7`: 7, `jul`: 7, `july`: 7,
-		`8`: 8, `aug`: 8, `august`: 8,
-		`9`: 9, `sep`: 9, `september`: 9,
+		`1`: 1, `01`: 1, `jan`: 1, `january`: 1,
+		`2`: 2, `02`: 2, `feb`: 2, `february`: 2,
+		`3`: 3, `03`: 3, `mar`: 3, `march`: 3,
+		`4`: 4, `04`: 4, `apr`: 4, `april`: 4,
+		`5`: 5, `05`: 5, `may`: 5,
+		`6`: 6, `06`: 6, `jun`: 6, `june`: 6,
+		`7`: 7, `07`: 7, `jul`: 7, `july`: 7,
+		`8`: 8, `08`: 8, `aug`: 8, `august`: 8,
+		`9`: 9, `09`: 9, `sep`: 9, `september`: 9,
 		`10`: 10, `oct`: 10, `october`: 10,
 		`11`: 11, `nov`: 11, `november`: 11,
 		`12`: 12, `dec`: 12, `december`: 12,

cronexpr_test.go

@@ -209,6 +209,17 @@ var crontests = []crontest{
 		},
 	},
 
+	// Zero padded months
+	{
+		"0 0 * 04 * *",
+		"Mon 2006-01-02 15:04",
+		[]crontimes{
+			{"2013-09-02 00:00:00", "Tue 2014-04-01 00:00"},
+			{"2014-04-03 03:00:00", "Fri 2014-04-04 00:00"},
+			{"2014-08-15 00:00:00", "Wed 2015-04-01 00:00"},
+		},
+	},
+
 	// TODO: more tests
 }