As you have mentioned java 8 is been deprecated so You can force the analysis with Java 8 temporarily by setting the property

‘sonar.scanner.force-deprecated-java-version’ to ‘true’.

in POM file like below

<properties>
    <java.version>1.8</java.version>
    <sonar.scanner.force-deprecated-java-version>true</sonar.scanner.force-deprecated-java-version>
</properties>

hope this will work.

You can find more information here: sonar up-comings.

cheers.