Fix a typo in the cluster setup doc

This was reported through the mailing list.
The source is at hadoop-common-project/hadoop-common/src/site/markdown/ClusterSetup.md.

> On Sat, May 9, 2015 at 1:10 PM, 有江香織 <k.arie@miningbrownie.co.jp> wrote:
>> To whom this may concern,
>>
>>
>> I found a dead link and typo.
>>
>> Could I ask you to help me out with fixing that problem?
>>
>>
>> + dead link: http://www.apache.org/contact.html
>> + typo:
>> URL:
>> http://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/ClusterSetup.html
>> + before: YARN damones
>> + after: YARN daemons
>>
>>
>> Sincerely,