Allow for null state on filtering milestones

app/src/main/java/com/commit451/gitlab/api/GitLabService.kt

@@ -145,7 +145,7 @@ interface GitLabService {
     @GET(API_VERSION + "/projects/{id}/milestones")
     fun getMilestones(@Path("id") projectId: Long,
-                      @Query("state") state: String): Single<Response<List<Milestone>>>
+                      @Query("state") state: String?): Single<Response<List<Milestone>>>
     @GET
     fun getMilestones(@Url url: String): Single<Response<List<Milestone>>>

app/src/main/java/com/commit451/gitlab/fragment/MilestonesFragment.kt

@@ -51,7 +51,7 @@ class MilestonesFragment : ButterKnifeFragment() {
     lateinit var adapterMilestones: MilestoneAdapter
     lateinit var layoutManagerMilestones: LinearLayoutManager
-    lateinit var state: String
+    var state: String? = null
     lateinit var states: Array<String>
     var project: Project? = null
     var loading = false