Fix bad shorthand parse

In crontab.go, we rely on https://github.com/gorhill/cronexpr to parse
cron expressions, and to tell us when they're invalid.

To choose what to feed into cronexpr, we pick out a number of tokens
from the start of the cron line that might yield a valid cron
expression, starting with the most tokens (we try 7, then 6, then 5,
then 1). When we hit a valid cron expression, we stop there.

Unfortunately, I overlooked the fact that cronexpr isn't exactly
designed for this use case, and will not return an error when
passed e.g. `@hourly foo` (it just ignores `foo` in this case).

This is a problem if the user is using a shorthand cron expression and a
command with 4 or more tokens: in this case, we'll attempt to parse the
shorthand and the 4 first tokens in cronexpr, which will work (it'll
ignore the tokens altogether), and we'll be left with a truncated
command (missing the 4 first tokens).

The ideal fix would be to have cronexpr reject this invalid expression
for us, so I'm opening a PR there. In the meantime, I'm also opening
this PR in Supercronic with a fix my fork of cronexpr.

Gopkg.toml

@@ -23,7 +23,8 @@
 
 [[constraint]]
   name = "github.com/gorhill/cronexpr"
-  version = "~1.0.0"
+  branch = "strict"
+  source = "github.com/krallin/cronexpr"
 
 [[constraint]]
   name = "github.com/sirupsen/logrus"

crontab/crontab.go

@@ -36,7 +36,7 @@ func parseJobLine(line string) (*CrontabLine, error) {
 		// TODO: Should receive a logger?
 		logrus.Debugf("try parse(%d): %s[0:%d] = %s", count, line, scheduleEnds, line[0:scheduleEnds])
 
-		expr, err := cronexpr.Parse(line[:scheduleEnds])
+		expr, err := cronexpr.ParseStrict(line[:scheduleEnds])
 
 		if err != nil {
 			continue

crontab/crontab_test.go

@@ -229,6 +229,24 @@ var parseCrontabTestCases = []struct {
 		},
 	},
 
+	{
+		"@hourly foo1 foo2 foo3 foo4 foo5 foo6",
+		&Crontab{
+			Context: &Context{
+				Shell:   "/bin/sh",
+				Environ: map[string]string{},
+			},
+			Jobs: []*Job{
+				{
+					CrontabLine: CrontabLine{
+						Schedule: "@hourly",
+						Command:  "foo1 foo2 foo3 foo4 foo5 foo6",
+					},
+				},
+			},
+		},
+	},
+
 	// Failure cases
 	{"* foo \n", nil},
 	{"* some * * *  more\n", nil},