Fix typo in comment: mail -> main

cmd/kube-controller-manager/app/controllermanager.go

@@ -41,7 +41,7 @@ import (
 	"github.com/spf13/pflag"
 )
 
-// CMServer is the mail context object for the controller manager.
+// CMServer is the main context object for the controller manager.
 type CMServer struct {
 	Port                    int
 	Address                 util.IP