Update keyspace.rb

I am getting this error: 
```
`eval': undefined method `connect' for Cassandra:Module (NoMethodError)
	from /Users/gsaylor/.rvm/rubies/ruby-2.1.1/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
	from /Users/gsaylor/.rvm/gems/ruby-2.1.1/bundler/gems/cequel-40895942b499/lib/cequel/metal/keyspace.rb:251:in `cluster'
	from /Users/gsaylor/.rvm/gems/ruby-2.1.1/bundler/gems/cequel-40895942b499/lib/cequel/metal/keyspace.rb:157:in `block in client'
```
Not sure if this is a good fix?

This happens via a call like:
```
Cequel::Record.connection.client()
```