Upgrade to Kotlin 1.2

apiVersion and languageVersion options are set to 1.1
in order to avoid incompatibilities with Kotlin 1.1
based projects.

Closes gh-11235

spring-boot-project/spring-boot-parent/pom.xml

@@ -287,6 +287,8 @@
 					<version>${kotlin.version}</version>
 					<configuration>
 						<jvmTarget>${java.version}</jvmTarget>
+						<apiVersion>1.1</apiVersion>
+						<languageVersion>1.1</languageVersion>
 					</configuration>
 				</plugin>
 				<plugin>