support java 10
At least archlinux has openjdk-10 packages and pulls it as default dependency when installing the android-sdk
Our java search regexes can't handle java10 being there: https://gitlab.com/fdroid/fdroidserver/blob/master/fdroidserver/common.py#L207 and https://gitlab.com/fdroid/fdroidserver/blob/master/fdroidserver/common.py#L162 and maybe other places as well.