test: add servlet for Tomcat8

Author: ReaJason

integration-test/src/test/java/com/reajason/javaweb/integration/tomcat/Tomcat8ContainerTest.java

@@ -55,6 +55,7 @@ static Stream<Arguments> casesProvider() {
         Server server = Server.Tomcat;
         List<String> supportedShellTypes = List.of(
                 ShellType.FILTER,
+                ShellType.SERVLET,
                 ShellType.LISTENER,
                 ShellType.VALVE,
                 ShellType.WEBSOCKET,