Use underline instead of dash in tomcat properties

Closes gh-10256

Author: aconstantin

spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -2463,8 +2463,8 @@ by adding some entries to `application.properties`, e.g.
 
 [source,properties,indent=0]
 ----
-	server.tomcat.remote_ip_header=x-forwarded-for
-	server.tomcat.protocol_header=x-forwarded-proto
+	server.tomcat.remote-ip-header=x-forwarded-for
+	server.tomcat.protocol-header=x-forwarded-proto
 ----
 
 (The presence of either of those properties will switch on the valve. Or you can add the