Fix format string.

Change-Id: I99b3e2b63cb249b12d09cf3bccbb55226fab0cbe

populate/e2e_test.go

diff --git a/populate/e2e_test.go b/populate/e2e_test.go
index c57e78c..6bbcddc 100644
--- a/populate/e2e_test.go
+++ b/populate/e2e_test.go
@@ -235,7 +235,7 @@
 	if _, changed, err := Checkout(m1, ws); err != nil {
 		t.Fatalf("Checkout(m1): %v", err)
 	} else if len(changed) > 0 {
-		t.Errorf("Got changed files %v relative to broken link.")
+		t.Errorf("Got changed files %v relative to broken link", changed)
 	}
 }