Makes mock return non-null types.

Since `Mockito.mock` is a Java function it returns a Kotlin platform type.  By adding an explicit return type to the wrapper, the kotlin version of `mock` will now return a non-platform type.  In this case, we know that `Mockito.mock` doesn't return null so we can safely make the wrapper return a non-null type.  We add the `!!` to make it clear to the reader our intent is to strip the platform type at this point, and also make the Kotlin compiler add an explicit null-check "just in case" before returning from the kotlin `mock` method.

Author: Micah Zoltu

mockito-kotlin/src/main/kotlin/com/nhaarman/mockito_kotlin/Mockito.kt

@@ -69,10 +69,10 @@ inline fun <reified T : Any> isA() = Mockito.isA(T::class.java)
 inline fun <reified T : Any> isNotNull() = Mockito.isNotNull(T::class.java)
 inline fun <reified T : Any> isNull(): T? = Mockito.isNull(T::class.java)
 
-inline fun <reified T : Any> mock() = Mockito.mock(T::class.java)
-inline fun <reified T : Any> mock(defaultAnswer: Answer<Any>) = Mockito.mock(T::class.java, defaultAnswer)
-inline fun <reified T : Any> mock(s: MockSettings) = Mockito.mock(T::class.java, s)
-inline fun <reified T : Any> mock(s: String) = Mockito.mock(T::class.java, s)
+inline fun <reified T : Any> mock(): T = Mockito.mock(T::class.java)!!
+inline fun <reified T : Any> mock(defaultAnswer: Answer<Any>): T = Mockito.mock(T::class.java, defaultAnswer)!!
+inline fun <reified T : Any> mock(s: MockSettings): T = Mockito.mock(T::class.java, s)!!
+inline fun <reified T : Any> mock(s: String): T = Mockito.mock(T::class.java, s)!!
 
 fun mockingDetails(toInspect: Any) = Mockito.mockingDetails(toInspect)
 fun never() = Mockito.never()
@@ -99,4 +99,4 @@ fun <T> verifyNoMoreInteractions(vararg mocks: T) = Mockito.verifyNoMoreInteract
 fun verifyZeroInteractions(vararg mocks: Any) = Mockito.verifyZeroInteractions(*mocks)
 
 fun <T> whenever(methodCall: T) = Mockito.`when`(methodCall)
-fun withSettings() = Mockito.withSettings()
+fun withSettings() = Mockito.withSettings()