release version 1.8 not supported

This should work

<maven.compiler.release>8</maven.compiler.release>

since the <release> attribute works with the major versions of releases only.

By, the way this is assuming that this is a parameter used in the actual compiler-plugin configuration somewhat like :

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <configuration>
        <release>${maven.compiler.release}</release>
    </configuration>
</plugin>