Download links are outdate @ flintlib.org

`md5sum` of github vs flintlib.org
```
b172ad8fc59cbb2fa2f2ab31bb3c61fd  flint-3.1.0(1).tar.gz
eab82c770768f0ab9e32a7b3cfc4d5fd  flint-3.1.0(1).zip
fcc36930b05da464c1a1a49b50290869  flint-3.1.0.tar.gz
cd1cb6ec3f27d88063a332aa637edd3a  flint-3.1.0.zip
```
the `(1)` version is from flintlib.org