'Change greeting from 'Hello World!' to 'Hello Marvin!' and update test'

Author: Marvin

main.go

@@ -41,6 +41,6 @@ func main() {
 }
 
 func greeting() string {
-	greeting := "Greetings Daggernauts!"
+	greeting := "Hello Marvin!"
 	return fmt.Sprintf("{\"greeting\":\"%s\"}", greeting)
 }