Update module stretchr/testify to v1.5.1

Author: renovate-bot

go.mod

@@ -50,7 +50,7 @@ require (
 	github.com/shirou/gopsutil v0.0.0-20190901111213-e4ec7b275ada
 	github.com/sirupsen/logrus v1.4.2
 	github.com/spf13/viper v1.6.2
-	github.com/stretchr/testify v1.4.0
+	github.com/stretchr/testify v1.5.1
 	github.com/stvp/rollbar v0.5.1
 	github.com/stvp/tempredis v0.0.0-20181119212430-b82af8480203 // indirect
 	github.com/urfave/negroni v1.0.0