Bump cassandra-driver-core to 2.0.5.

A couple of severe bugs were closed in 2.0.4 (see [changelog](https://datastax-oss.atlassian.net/browse/JAVA?selectedTab=com.atlassian.jira.jira-projects-plugin:changelog-panel)).  My team update to 2.0.5 and thought the pull request can save you a couple of keystrokes.