Restore jvmTarget 1.6 for scripting libraries that could be used externally

#KT-29319 fixed

libraries/scripting/intellij/build.gradle.kts

@@ -4,6 +4,8 @@ plugins {
     id("jps-compatible")
 }
 
+jvmTarget = "1.6"
+
 dependencies {
     compile(project(":kotlin-script-runtime"))
     compile(kotlinStdlib())

libraries/scripting/jvm-host/build.gradle.kts

@@ -4,6 +4,8 @@ plugins {
     id("jps-compatible")
 }
 
+jvmTarget = "1.6"
+
 dependencies {
     compile(project(":kotlin-script-runtime"))
     compile(kotlinStdlib())