bump kotlin version

asurkov · asurkov · commit aa5c5a16a4cb · 2018-04-10T20:05:01.000-04:00
diff --git a/kotlin/build.gradle b/kotlin/build.gradle
@@ -2,7 +2,7 @@
 
 buildscript {
     ext {
-        kotlin_version = '1.1.51'
+        kotlin_version = '1.2.31'
     }
     repositories {
         mavenCentral()
