Merge pull request #782 from arkivanov/ValueCallback-fun-interface

Make ValueCallback a fun interface

Author: CherryPerry

reaktive/src/commonMain/kotlin/com/badoo/reaktive/base/ValueCallback.kt

@@ -3,7 +3,7 @@ package com.badoo.reaktive.base
 /**
  * A common callback for listening for values
  */
-interface ValueCallback<in T> {
+fun interface ValueCallback<in T> {
 
     /**
      * Delivers values to the host (typically an [Observer])