[goldpush] Add new line at the end of error message.

Change-Id: I7286c68876aec6d330fb62de1a2a352baf7d07a4
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/254036
Reviewed-by: Leandro Lovisolo <lovisolo@google.com>
Commit-Queue: Leandro Lovisolo <lovisolo@google.com>
Auto-Submit: Leandro Lovisolo <lovisolo@google.com>
diff --git a/golden/cmd/goldpushk/main.go b/golden/cmd/goldpushk/main.go
index 6c9c4e4..8015793 100644
--- a/golden/cmd/goldpushk/main.go
+++ b/golden/cmd/goldpushk/main.go
@@ -151,7 +151,7 @@
 	// Read environment variables.
 	skiaInfraRoot, ok := os.LookupEnv(skiaInfraRootEnvVar)
 	if !ok {
-		fmt.Printf("Error: environment variable %s not set.", skiaInfraRootEnvVar)
+		fmt.Printf("Error: environment variable %s not set.\n", skiaInfraRootEnvVar)
 		os.Exit(1)
 	}