use re_path instead of deprecated url method

[FabienArcellier]

use re_path instead of deprecated url method

For older versions of django, we use an alternate code path to retain support. The automatic tests are running correctly on python 2.7 with django 1.1 and python 3.8 with django 4.1.3

[FabienArcellier]

I had an issue with coveralls, one of the test dependency only on python3.7. I have updated to the last version that support python 2.7 without success. If we want to move over this issue on CI, we have either to drop the support of python 2.7 and django 3.1, either remove the check on python 3.7 on CI, either remove the usage of coverall.