Remove 'SecondsOrDuration' for check_interval

Now requires an explicit duration unit. Eg. 30s

monitor.go

@@ -11,9 +11,9 @@ import (
 // Monitor represents a particular periodic check of a command
 type Monitor struct { //nolint:maligned
 	// Config values
-	AlertAfter    int16             `yaml:"alert_after"`
-	AlertEvery    *int16            `yaml:"alert_every"`
-	CheckInterval SecondsOrDuration `yaml:"check_interval"`
+	AlertAfter    int16         `yaml:"alert_after"`
+	AlertEvery    *int16        `yaml:"alert_every"`
+	CheckInterval time.Duration `yaml:"check_interval"`
 	Name          string
 	AlertDown     []string `yaml:"alert_down"`
 	AlertUp       []string `yaml:"alert_up"`
@@ -45,7 +45,7 @@ func (monitor Monitor) ShouldCheck() bool {
 
 	sinceLastCheck := time.Since(monitor.lastCheck)
 
-	return sinceLastCheck >= monitor.CheckInterval.Value()
+	return sinceLastCheck >= monitor.CheckInterval
 }
 
 // Check will run the command configured by the Monitor and return a status