Use deprecated JsonParser#parse since gson is not upgraded

Change-Id: I03020921d9d31326a4fa0af09ff0a56dfc1595d7
diff --git a/src/main/java/com/googlesource/gerrit/plugins/ratelimiter/RateLimiterProcessing.java b/src/main/java/com/googlesource/gerrit/plugins/ratelimiter/RateLimiterProcessing.java
index 8f23613..8e11de9 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/ratelimiter/RateLimiterProcessing.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/ratelimiter/RateLimiterProcessing.java
@@ -67,7 +67,7 @@
         .sorted(Map.Entry.comparingByValue())
         .map(this::getJsonObjectString)
         .forEach(permitList::add);
-    return gson.toJson(JsonParser.parseString(permitList.toString()));
+    return gson.toJson(new JsonParser().parse(permitList.toString()));
   }
 
   private String getJsonObjectString(Map.Entry<String, RateLimiter> entry) {