Upgrade to Jetty 9.4.18.v20190429

Closes gh-16761

spring-boot-dependencies/pom.xml

@@ -111,7 +111,7 @@
 		<jedis.version>2.9.3</jedis.version>
 		<jersey.version>2.25.1</jersey.version>
 		<jest.version>2.0.4</jest.version>
-		<jetty.version>9.4.16.v20190411</jetty.version>
+		<jetty.version>9.4.18.v20190429</jetty.version>
 		<jetty-jsp.version>2.2.0.v201112011158</jetty-jsp.version>
 		<jetty-el.version>8.0.33</jetty-el.version>
 		<jms-api.version>1.1-rev-1</jms-api.version>