Migrate Sirupsen to sirupsen.

cmd/traefik/traefik.go

@@ -10,7 +10,6 @@ import (
 	"strings"
 	"time"
 
-	"github.com/Sirupsen/logrus"
 	"github.com/cenk/backoff"
 	"github.com/containous/flaeg"
 	"github.com/containous/staert"
@@ -28,6 +27,7 @@ import (
 	"github.com/containous/traefik/types"
 	"github.com/containous/traefik/version"
 	"github.com/coreos/go-systemd/daemon"
+	"github.com/sirupsen/logrus"
 )
 
 func main() {