Update Mockito kotlin package

[ken-kentan]

Hello/bonjour,

What?

I update Testing.kt's package reference from old to new package name

Why?

The package com.nhaarman.mockitokotlin2:mockito-kotlin was moved to org.mockito.kotlin:mockito-kotlin

How?

Update group name from com.nhaarman.mockitokotlin2 to org.mockito.kotlin

Testing?

I run gradle check in /plugins folder.