ZOOKEEPER-3056: fix documentation.

snapshot.trust.empty can be used in both zoo.cfg file (with name snapshot.trust.empty), and as a system property (with name zookeeper.snapshot.trust.empty).

Author: Michael Han <lhan@twitter.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>

Closes #1178 from hanm/ZOOKEEPER-3056

zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md

@@ -1035,7 +1035,7 @@ property, when available, is noted below.
     By default, this feautre is disabled, set "true" to enable it.
 
 * *snapshot.trust.empty* :
-    (Java system property only: **zookeeper.snapshot.trust.empty**)
+    (Java system property: **zookeeper.snapshot.trust.empty**)
     **New in 3.5.6:**
     This property controls whether or not ZooKeeper should treat missing
     snapshot files as a fatal state that can't be recovered from.