Back to JDK8. Try again in a few months.

.travis.yml

@@ -5,7 +5,7 @@ addons:
         organization: "bentobox-world"
 
 jdk:
-    - openjdk11
+    - openjdk8
         
 script:
     #- sonar-scanner

pom.xml

@@ -321,7 +321,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.8.1</version>
                 <configuration>
-                    <release>8</release>
+                    <source>${java.version}</source>
+                    <target>${java.version}</target>
                 </configuration>
             </plugin>
             <plugin>
@@ -338,16 +339,18 @@
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-javadoc-plugin</artifactId>
                 <version>3.1.1</version>
-                <configuration>
+                <configuration>                
+                    <source>8</source>
                     <show>private</show>
                     <failOnError>false</failOnError>
                     <additionalJOption>-Xdoclint:none</additionalJOption>
                     <!-- To compile with Java 11, this tag may be required -->
-                    <javadocExecutable>${java.home}/bin/javadoc</javadocExecutable>
+                    <!--  <javadocExecutable>${java.home}/bin/javadoc</javadocExecutable>-->
                 </configuration>
                 <executions>
                     <execution>
                         <id>attach-javadocs</id>
+                        <phase>install</phase>
                         <goals>
                             <goal>jar</goal>
                         </goals>