Remove omittable "()"

Author: komainu8

_overviews/tutorials/scala-for-java-programmers.md

@@ -332,7 +332,7 @@ We can call overridden `toString` method as below.
     object ComplexNumbers {
       def main(args: Array[String]): Unit = {
         val c = new Complex(1.2, 3.4)
-        println("Overridden toString(): " + c.toString())
+        println("Overridden toString(): " + c.toString)
       }
     }