Update Jetty to 9.4.20.v20190813
<!-- Skip because of problems with Java 8 -->
<animal.sniffer.skip>true</animal.sniffer.skip>
<felix.java.version>8</felix.java.version>
- <jetty.version>9.4.19.v20190610</jetty.version>
+ <jetty.version>9.4.20.v20190813</jetty.version>
</properties>
<build>
