Fix how the rule is displayed in the error message.

Bug: 204001941
Test: internal
Change-Id: I19c73356cc305ec7a6dfd3bddbde775ef9ca4953
diff --git a/mk2rbc/mk2rbc.go b/mk2rbc/mk2rbc.go
index 99008d1..fb72638 100644
--- a/mk2rbc/mk2rbc.go
+++ b/mk2rbc/mk2rbc.go
@@ -1466,7 +1466,7 @@
 			handled = false
 		}
 	default:
-		ctx.errorf(x, "unsupported line %s", x.Dump())
+		ctx.errorf(x, "unsupported line %s", strings.ReplaceAll(x.Dump(), "\n", "\n#"))
 	}
 	return handled
 }