jar {
    manifest {
        mainAttributes( 'Main-Class': 'org.hibernate.Version' )

        instructionFirst 'Import-Package',
...
            'javax.persistence;version="2.1.0"',
...
    }
}

jar {
    manifest {
        mainAttributes( 'Main-Class': 'org.hibernate.Version' )

        instructionFirst 'Import-Package',
...
            'javax.persistence;version="' + project.ext.jpaVersion + '.0"',
...
    }
}

interface JpaVersion {
    /** The *normal* name (1.0, 2.0, ..) */
    String getName();
    /** OSGi requires a certain format to naming versions */
    default String getOsgiName() {
        return getName() + ".0";
    }
}

...

ext {
    jpaVersion = new JpaVersion() { () -> '2.2' }
}

jar {
    manifest {
        mainAttributes( 'Main-Class': 'org.hibernate.Version' )

        instructionFirst 'Import-Package',
...
            'javax.persistence;version="' + project.ext.jpaVersion.osgiName + '"',
...
    }
}