[SPEC] indices.upgrade wait_for_completion defaults to false

https://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/rest/action/admin/indices/upgrade/RestUpgradeAction.java#L93

The docs are correct: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/indices-upgrade.html#upgrade-parameters, but the description in the spec is wrong.