Only enable soft-deletes in 6.5 or later

Author: dnhatn

server/src/main/java/org/elasticsearch/index/IndexSettings.java

@@ -407,7 +407,7 @@ public IndexSettings(final IndexMetaData indexMetaData, final Settings nodeSetti
         generationThresholdSize = scopedSettings.get(INDEX_TRANSLOG_GENERATION_THRESHOLD_SIZE_SETTING);
         mergeSchedulerConfig = new MergeSchedulerConfig(this);
         gcDeletesInMillis = scopedSettings.get(INDEX_GC_DELETES_SETTING).getMillis();
-        softDeleteEnabled = version.onOrAfter(Version.V_6_4_0) && scopedSettings.get(INDEX_SOFT_DELETES_SETTING);
+        softDeleteEnabled = version.onOrAfter(Version.V_6_5_0) && scopedSettings.get(INDEX_SOFT_DELETES_SETTING);
         softDeleteRetentionOperations = scopedSettings.get(INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING);
         warmerEnabled = scopedSettings.get(INDEX_WARMER_ENABLED_SETTING);
         maxResultWindow = scopedSettings.get(MAX_RESULT_WINDOW_SETTING);