Fix generics warnings triggered by upgrade to Tomcat 7.0.55

See changes made in revision 1602507 [1]

[1] https://svn.apache.org/viewvc?view=revision&revision=1602507

spring-boot/src/main/java/org/springframework/boot/context/embedded/tomcat/TomcatEmbeddedServletContainerFactory.java

@@ -219,7 +219,7 @@ public class TomcatEmbeddedServletContainerFactory extends
 		connector.setPort(port);
 		if (connector.getProtocolHandler() instanceof AbstractProtocol) {
 			if (getAddress() != null) {
-				((AbstractProtocol) connector.getProtocolHandler())
+				((AbstractProtocol<?>) connector.getProtocolHandler())
 						.setAddress(getAddress());
 			}
 		}