Fix comment for mocks.NewConsumer

The config object is not unused and can in fact be set when calling the
NewConsumer constructor. This commit updates the function's description
to reflect that.

mocks/consumer.go

@@ -20,7 +20,7 @@ type Consumer struct {
 
 // NewConsumer returns a new mock Consumer instance. The t argument should
 // be the *testing.T instance of your test method. An error will be written to it if
-// an expectation is violated. The config argument is currently unused and can be set to nil.
+// an expectation is violated. The config argument can be set to nil.
 func NewConsumer(t ErrorReporter, config *sarama.Config) *Consumer {
 	if config == nil {
 		config = sarama.NewConfig()