added kotlin plugin for successfull compilation

proj.android-studio/app/build.gradle

@@ -1,4 +1,5 @@
 apply plugin: 'com.android.application'
+apply plugin: 'kotlin-android'
 
 android {
     compileSdkVersion 28
@@ -45,4 +46,6 @@ dependencies {
     implementation 'com.android.support:appcompat-v7:28+'
 
     implementation project(':SalmonEngineAndroid')
+
+    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
 }