Ensure Kotlin 1.3 compatibility.

Closes #1411

Author: mp911de

parent/pom.xml

@@ -1109,6 +1109,8 @@
 				<version>${kotlin}</version>
 				<configuration>
 					<jvmTarget>${source.level}</jvmTarget>
+					<apiVersion>1.3</apiVersion>
+					<languageVersion>1.3</languageVersion>
 					<skip>${maven.kotlin.skip}</skip>
 				</configuration>
 				<executions>