Corrected the alias for the link of HBASE-6580

Previous versions of this guide discussed `HTablePool`, which was deprecated in HBase 0.94, 0.95, and 0.96, and removed in 0.98.1, by link:https://issues.apache.org/jira/browse/HBASE-6580[HBASE-6500], or `HConnection`, which is deprecated in HBase 1.0 by `Connection`.
Please use link:http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/client/Connection.html[Connection] instead.