Fix typescript error - RouterState not exported

Change-Id: I887f9d568fe73d7f7cf359bd0b9c58fc8829af9c
diff --git a/polygerrit-ui/app/services/router/router-model.ts b/polygerrit-ui/app/services/router/router-model.ts
index b2d99480..201cb3f 100644
--- a/polygerrit-ui/app/services/router/router-model.ts
+++ b/polygerrit-ui/app/services/router/router-model.ts
@@ -35,7 +35,7 @@
   SETTINGS = 'settings',
 }
 
-interface RouterState {
+export interface RouterState {
   view?: GerritView;
   changeNum?: NumericChangeId;
   patchNum?: PatchSetNum;