Allow awaitResponse() to be called with nullable type parameter.

retrofit/src/main/java/retrofit2/KotlinExtensions.kt

@@ -83,7 +83,7 @@ suspend fun <T : Any> Call<T?>.await(): T? {
   }
 }
 
-suspend fun <T : Any> Call<T>.awaitResponse(): Response<T> {
+suspend fun <T> Call<T>.awaitResponse(): Response<T> {
   return suspendCancellableCoroutine { continuation ->
     continuation.invokeOnCancellation {
       cancel()