[cassandra] Bump to current stable version.

The 2.0.0-rc2 driver has a bug
(https://datastax-oss.atlassian.net/browse/JAVA-254) which gets
triggered when querying through presto.

The exception occurs because the driver attempts to query a table that
no longer exists, and fails.

Cassandra 2.1.0 is the current stable release, so it's probably time to
catch up.

The full exception looks like this:

```
Query 20140919_144621_02958_k67kx failed: replicate_on_write is not a column defined in this metadata
java.lang.IllegalArgumentException: replicate_on_write is not a column defined in this metadata
	at com.datastax.driver.core.ColumnDefinitions.getAllIdx(ColumnDefinitions.java:273)
	at com.datastax.driver.core.ColumnDefinitions.getFirstIdx(ColumnDefinitions.java:279)
	at com.datastax.driver.core.Row.getBool(Row.java:117)
	at com.datastax.driver.core.TableMetadata$Options.<init>(TableMetadata.java:474)
	at com.datastax.driver.core.TableMetadata.build(TableMetadata.java:107)
	at com.datastax.driver.core.Metadata.buildTableMetadata(Metadata.java:128)
	at com.datastax.driver.core.Metadata.rebuildSchema(Metadata.java:89)
	at com.datastax.driver.core.ControlConnection.refreshSchema(ControlConnection.java:259)
	at com.datastax.driver.core.ControlConnection.tryConnect(ControlConnection.java:214)
	at com.datastax.driver.core.ControlConnection.reconnectInternal(ControlConnection.java:161)
	at com.datastax.driver.core.ControlConnection.connect(ControlConnection.java:77)
	at com.datastax.driver.core.Cluster$Manager.init(Cluster.java:890)
	at com.datastax.driver.core.Cluster$Manager.newSession(Cluster.java:910)
	at com.datastax.driver.core.Cluster$Manager.access$200(Cluster.java:806)
	at com.datastax.driver.core.Cluster.connect(Cluster.java:158)
	at com.facebook.presto.cassandra.CassandraSession$1.load(CassandraSession.java:95)
	at com.facebook.presto.cassandra.CassandraSession$1.load(CassandraSession.java:90)
	at com.google.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3524)
	at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2317)
	at com.google.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2280)
	at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2195)
	at com.google.common.cache.LocalCache.get(LocalCache.java:3934)
	at com.google.common.cache.LocalCache.getOrLoad(LocalCache.java:3938)
	at com.google.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4821)
	at com.facebook.presto.cassandra.CassandraSession.getSession(CassandraSession.java:115)
	at com.facebook.presto.cassandra.CassandraSession.executeWithSession(CassandraSession.java:435)
	at com.facebook.presto.cassandra.CassandraSession.executeQuery(CassandraSession.java:124)
	at com.facebook.presto.cassandra.CassandraRecordCursor.<init>(CassandraRecordCursor.java:42)
	at com.facebook.presto.cassandra.CassandraRecordSet.cursor(CassandraRecordSet.java:55)
	at com.facebook.presto.operator.RecordProjectOperator.<init>(RecordProjectOperator.java:45)
	at com.facebook.presto.split.RecordSetDataStreamProvider.createNewDataStream(RecordSetDataStreamProvider.java:40)
	at com.facebook.presto.split.DataStreamManager.createNewDataStream(DataStreamManager.java:58)
	at com.facebook.presto.operator.AbstractScanFilterAndProjectOperator.addSplit(AbstractScanFilterAndProjectOperator.java:95)
	at com.facebook.presto.operator.Driver.processNewSource(Driver.java:251)
	at com.facebook.presto.operator.Driver.processNewSources(Driver.java:216)
	at com.facebook.presto.operator.Driver.access$300(Driver.java:52)
	at com.facebook.presto.operator.Driver$DriverLockResult.close(Driver.java:491)
	at com.facebook.presto.operator.Driver.updateSource(Driver.java:194)
	at com.facebook.presto.execution.SqlTaskExecution$DriverSplitRunnerFactory.createDriver(SqlTaskExecution.java:585)
	at com.facebook.presto.execution.SqlTaskExecution$DriverSplitRunnerFactory.access$1700(SqlTaskExecution.java:552)
	at com.facebook.presto.execution.SqlTaskExecution$DriverSplitRunner.processFor(SqlTaskExecution.java:673)
	at com.facebook.presto.execution.TaskExecutor$PrioritizedSplitRunner.process(TaskExecutor.java:444)
	at com.facebook.presto.execution.TaskExecutor$Runner.run(TaskExecutor.java:578)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)
```