Update Samples and Guides to use Lettuce

Favor lettuce because of multiplexing and improved scalability.
Using lettuce requires a fixed number of connections hence using
lettuce improves application scalability.

Fixes gh-652

samples/websocket/src/main/java/sample/config/DataSourceConfig.java

@@ -20,7 +20,7 @@ import javax.sql.DataSource;
 
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
+import org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory;
 import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;
 import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType;
 
@@ -34,7 +34,7 @@ public class DataSourceConfig {
 	}
 
 	@Bean
-	public JedisConnectionFactory connectionFactory() {
-		return new JedisConnectionFactory();
+	public LettuceConnectionFactory connectionFactory() {
+		return new LettuceConnectionFactory();
 	}
 }