Upgrade to Undertow 1.3.18.Final

Closes gh-5182

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -157,7 +157,7 @@
 		<thymeleaf-layout-dialect.version>1.3.1</thymeleaf-layout-dialect.version>
 		<thymeleaf-extras-data-attribute.version>1.3</thymeleaf-extras-data-attribute.version>
 		<tomcat.version>8.0.32</tomcat.version>
-		<undertow.version>1.3.17.Final</undertow.version>
+		<undertow.version>1.3.18.Final</undertow.version>
 		<velocity.version>1.7</velocity.version>
 		<velocity-tools.version>2.0</velocity-tools.version>
 		<webjars-hal-browser.version>9f96c74</webjars-hal-browser.version>