Adapt to changes in Gerrit core

index.onlineUpgrade was updated in I109da60a08 to be ternary. Update
ElasticIndexVersionManager to adapt to that change.

Change-Id: Ib650791fe94aba614024cbfb50e0b3a614367b91
diff --git a/src/main/java/com/google/gerrit/elasticsearch/ElasticIndexVersionManager.java b/src/main/java/com/google/gerrit/elasticsearch/ElasticIndexVersionManager.java
index f39a604..1578e85 100644
--- a/src/main/java/com/google/gerrit/elasticsearch/ElasticIndexVersionManager.java
+++ b/src/main/java/com/google/gerrit/elasticsearch/ElasticIndexVersionManager.java
@@ -52,7 +52,7 @@
         sitePaths,
         listeners,
         defs,
-        VersionManager.getOnlineUpgrade(cfg),
+        VersionManager.shouldPerformOnlineUpgrade(cfg),
         cfg.getBoolean("index", "reuseExistingDocuments", false));
     this.versionDiscovery = versionDiscovery;
     prefix = Strings.nullToEmpty(cfg.getString("elasticsearch", null, "prefix"));