feat(index): add primary param to Index (#625)

Author: aallam

src/main/scala/algolia/responses/Indices.scala

@@ -36,5 +36,6 @@ case class Index(
     fileSize: Int,
     lastBuildTimeS: Int,
     numberOfPendingTasks: Int,
-    pendingTask: Boolean
+    pendingTask: Boolean,
+    primary: Option[String] = None
 )