Update Mockito to 2.2.15

Author: nhaarman

mockito-kotlin/build.gradle

@@ -45,7 +45,7 @@ test.dependsOn testInlineMockito
 dependencies {
     compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
     compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "org.mockito:mockito-core:2.2.9"
+    compile "org.mockito:mockito-core:2.2.15"
 
     /* Tests */
     testCompile "junit:junit:4.12"