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-dependencies/pom.xml

@@ -106,7 +106,7 @@
 		<junit.version>4.12</junit.version>
 		<junit-jupiter.version>5.0.2</junit-jupiter.version>
 		<junit-platform.version>1.0.2</junit-platform.version>
-		<kotlin.version>1.1.61</kotlin.version>
+		<kotlin.version>1.2.0</kotlin.version>
 		<lettuce.version>5.0.1.RELEASE</lettuce.version>
 		<liquibase.version>3.5.3</liquibase.version>
 		<log4j2.version>2.10.0</log4j2.version>

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>