[ci] Go back to java8 in order to include scala in the release

.travis.yml

@@ -3,13 +3,13 @@ sudo: false
 addons:
   apt:
     packages:
-      - oracle-java9-installer
+      - oracle-java8-installer
   ssh_known_hosts:
     - web.sourceforge.net
 
 language: java
 
-jdk: oraclejdk9
+jdk: oraclejdk8
 
 env:
   global:

.travis/build-coveralls.sh

@@ -14,7 +14,6 @@ fi
 #
 # for java9: enable all modules.
 # coveralls plugin seems to need java.xml.bind module
-#
-echo "MAVEN_OPTS='-Xms1g -Xmx1g --add-modules java.se.ee'" > ${HOME}/.mavenrc
+# echo "MAVEN_OPTS='-Xms1g -Xmx1g --add-modules java.se.ee'" > ${HOME}/.mavenrc
 
 ./mvnw clean test jacoco:report coveralls:report -Pcoveralls -B -V

.travis/build-sonar.sh

@@ -14,8 +14,7 @@ fi
 #
 # for java9: enable all modules.
 # sonar plugin seems to need java.xml.bind module
-#
-echo "MAVEN_OPTS='-Xms1g -Xmx1g --add-modules java.se.ee'" > ${HOME}/.mavenrc
+# echo "MAVEN_OPTS='-Xms1g -Xmx1g --add-modules java.se.ee'" > ${HOME}/.mavenrc
 
 # Run the build, truncate output due to Travis log limits
 ./mvnw clean org.jacoco:jacoco-maven-plugin:prepare-agent package sonar:sonar -Dsonar.host.url=https://sonarcloud.io -Dsonar.login=${SONAR_TOKEN} -B -V

pom.xml

@@ -342,7 +342,6 @@ Additionally it includes CPD, the copy-paste-detector. CPD finds duplicated code
                     <configuration>
                         <source>${java.version}</source>
                         <target>${java.version}</target>
-                        <release>${java.version}</release>
                     </configuration>
                 </plugin>
                 <plugin>
@@ -480,7 +479,7 @@ Additionally it includes CPD, the copy-paste-detector. CPD finds duplicated code
                         <configuration>
                             <rules>
                                 <requireJavaVersion>
-                                    <version>[9,)</version>
+                                    <version>[1.8,)</version>
                                 </requireJavaVersion>
                             </rules>
                         </configuration>
@@ -939,6 +938,26 @@ Additionally it includes CPD, the copy-paste-detector. CPD finds duplicated code
             </modules>
         </profile>
 
+        <profile>
+            <id>jdk9-config</id>
+            <activation>
+                <jdk>[9,</jdk>
+            </activation>
+            <build>
+                <pluginManagement>
+                    <plugins>
+                        <plugin>
+                            <groupId>org.apache.maven.plugins</groupId>
+                            <artifactId>maven-compiler-plugin</artifactId>
+                            <configuration>
+                                <release>${java.version}</release>
+                            </configuration>
+                        </plugin>
+                    </plugins>
+                </pluginManagement>
+            </build>
+        </profile>
+
         <profile>
             <id>jdk9-disabled</id>
             <activation>