tools/principal: Fix a catastrophic usability issue

Change-Id: Ia2af178319a626fc69cdaf540b35dc31924f3b90
diff --git a/tools/principal/main.go b/tools/principal/main.go
index c3e4dce..666b4aa 100644
--- a/tools/principal/main.go
+++ b/tools/principal/main.go
@@ -594,7 +594,7 @@
 					return fmt.Errorf("AddToRoots failed: %v", err)
 				}
 			}
-			fmt.Fprintf(cmd.Stdout(), "Received blessings: %v", blessings)
+			fmt.Fprintf(cmd.Stdout(), "Received blessings: %v\n", blessings)
 			return nil
 		},
 	}