fix(security): update Jetty to 9.2.28.v20190418 and fix possible CVEs.

This update addressed the following CVEs:
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7656
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7657
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7658
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-12536
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-12538
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-10241
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-10246
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-10247

See for details:
- https://www.eclipse.org/lists/jetty-announce/msg00123.html
- https://webtide.com/indexing-listing-vulnerability-in-jetty/

Changelogs:
- https://github.com/eclipse/jetty.project/releases/tag/jetty-9.2.19.v20160908
- https://www.eclipse.org/lists/jetty-announce/msg00099.html
- https://www.eclipse.org/lists/jetty-announce/msg00100.html
- https://www.eclipse.org/lists/jetty-announce/msg00110.html
- https://github.com/eclipse/jetty.project/releases/tag/jetty-9.2.23.v20171218
- https://github.com/eclipse/jetty.project/releases/tag/jetty-9.2.24.v20180105
- https://www.eclipse.org/lists/jetty-announce/msg00116.html (EOL announcement)
- https://www.eclipse.org/lists/jetty-announce/msg00120.html
- https://github.com/eclipse/jetty.project/releases/tag/jetty-9.2.26.v20180806
- https://github.com/eclipse/jetty.project/releases/tag/jetty-9.2.27.v20190403
- https://www.eclipse.org/lists/jetty-announce/msg00130.html

Author: php-coder

pom.xml

@@ -518,7 +518,7 @@
 		<javax.validation.version>1.1.0.Final</javax.validation.version>
 
 		<!-- Redefine default value from spring-boot-dependencies (https://github.com/spring-projects/spring-boot/blob/v1.5.21.RELEASE/spring-boot-dependencies/pom.xml) -->
-		<jetty.version>9.2.18.v20160721</jetty.version>
+		<jetty.version>9.2.28.v20190418</jetty.version>
 
 		<!-- Don't forget to update version in the ResourceUrl class -->
 		<jquery.version>1.9.1</jquery.version>