Bump jetty-jspc-maven-plugin from 9.4.19.v20190610 to 9.4.26.v20200117

Bumps [jetty-jspc-maven-plugin](https://github.com/eclipse/jetty.project) from 9.4.19.v20190610 to 9.4.26.v20200117.
- [Release notes](https://github.com/eclipse/jetty.project/releases)
- [Commits](https://github.com/eclipse/jetty.project/compare/jetty-9.4.19.v20190610...jetty-9.4.26.v20200117)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

airsonic-main/pom.xml

@@ -669,7 +669,7 @@
             <plugin>
                 <groupId>org.eclipse.jetty</groupId>
                 <artifactId>jetty-jspc-maven-plugin</artifactId>
-                <version>9.4.19.v20190610</version>
+                <version>9.4.26.v20200117</version>
                 <executions>
                     <execution>
                         <id>jspc</id>