Update Kotlin version to 1.2.50

Author: nhaarman

mockito-kotlin/build.gradle

@@ -3,7 +3,7 @@ apply from: '../publishing.gradle'
 apply plugin: 'org.jetbrains.dokka'
 
 buildscript {
-    ext.kotlin_version = "1.2.20"
+    ext.kotlin_version = "1.2.50"
 
     repositories {
         mavenCentral()

tests/build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.2.20'
+    ext.kotlin_version = '1.2.50'
     ext.kotlin_version = System.getenv("KOTLIN_VERSION") ?: '1.0.7'
 
     repositories {