fix Print format calls

[cfal]

discovered when running go test:

./client.go:197:14: github.com/sirupsen/logrus.Warnf call has arguments but no formatting directives                                                                                                                                                                          
./client.go:203:14: github.com/sirupsen/logrus.Warnf call has arguments but no formatting directives
./main.go:163:14: fmt.Sprintf call has arguments but no formatting directives

./server.go:229:13: github.com/sirupsen/logrus.Errorf call has arguments but no formatting directives

[elisescu]

Thx