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/custom-cookie/src/main/java/sample/Config.java

@@ -17,7 +17,7 @@
 package sample;
 
 import org.springframework.context.annotation.Bean;
-import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
+import org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory;
 import org.springframework.session.data.redis.config.annotation.web.http.EnableRedisHttpSession;
 import org.springframework.session.web.http.CookieSerializer;
 import org.springframework.session.web.http.DefaultCookieSerializer;
@@ -26,8 +26,8 @@ import org.springframework.session.web.http.DefaultCookieSerializer;
 public class Config {
 
 	@Bean
-	public JedisConnectionFactory connectionFactory() {
-		return new JedisConnectionFactory();
+	public LettuceConnectionFactory connectionFactory() {
+		return new LettuceConnectionFactory();
 	}
 
 	// tag::cookie-serializer[]