update to Jetty 9.4 (#11411)

pom.xml

@@ -48,7 +48,7 @@
         <dependency.unpack.directory>${project.build.directory}/dependency-unpack</dependency.unpack.directory>
 
         <!-- Cannot use 9.3 or 9.4 because they sometimes reset the connection too early in case of errors -->
-        <jetty.version>9.2.9.v20150224</jetty.version>
+        <jetty.version>9.4.14.v20181114</jetty.version>
         <phantomjs.version>2.1.1</phantomjs.version>
     </properties>