Merge pull request #2911 from VMironiuk/fix/scala-tutorial/singleton-objects/companion-objects-code

Fix code in `Scala Tour > Singleton Objects > Companion Objects`

Author: Philippus

_tour/singleton-objects.md

@@ -104,7 +104,7 @@ An object with the same name as a class is called a _companion object_. Converse
 
 {% tab 'Scala 2' for=companion-object-circle %}
 ```scala
-import scala.math.pow
+import scala.math.{Pi, pow}
 
 case class Circle(radius: Double) {
   import Circle._
@@ -123,7 +123,7 @@ circle1.area
 
 {% tab 'Scala 3' for=companion-object-circle %}
 ```scala
-import scala.math.pow
+import scala.math.{Pi, pow}
 
 case class Circle(radius: Double):
   import Circle.*