leveldb: update doc to match what we test (#1691)

Author: pjfanning

persistence/src/main/resources/reference.conf

@@ -343,14 +343,14 @@ pekko.persistence.snapshot-store.proxy {
 # LevelDB persistence requires the following dependency declarations:
 #
 # SBT:
-#       "org.iq80.leveldb"            % "leveldb"          % "0.7"
+#       "org.iq80.leveldb"            % "leveldb"          % "0.12"
 #       "org.fusesource.leveldbjni"   % "leveldbjni-all"   % "1.8"
 #
 # Maven:
 #        <dependency>
 #            <groupId>org.iq80.leveldb</groupId>
 #            <artifactId>leveldb</artifactId>
-#            <version>0.7</version>
+#            <version>0.12</version>
 #        </dependency>
 #        <dependency>
 #            <groupId>org.fusesource.leveldbjni</groupId>