Update Buildpacks README to correct supported Java versions
Update Buildpacks README to correct supported Java versions

PiperOrigin-RevId: 306269267
Change-Id: I05d2af4ff95407d387cbcbdca51996eada58dd19

GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks