Upgrade to netty 3.5.8

closes elastic#2299.

Author: kimchy

pom.xml

@@ -140,7 +140,7 @@
         <dependency>
             <groupId>io.netty</groupId>
             <artifactId>netty</artifactId>
-            <version>3.5.7.Final</version>
+            <version>3.5.8.Final</version>
             <scope>compile</scope>
         </dependency>