Fix bootstrap 5 multiselect test (#125)

* bootstrap5

* update ci py version

* update tox python version

* update tox python version

* use , sperator in tox passenv

* use allowlist_externals

* add './' in allowlist_externals

* pin selenium version

* fix select2 test

* fix select2 test

* fix select2 multiple test

* fix select2 multiple test

* fix select2 X test

* fix selenium tests

* fix linting && use new python, pypy version

* fix flake8

* fix restructured text https://stackoverflow.com/a/39720161/1154966 does not work

* fix unofficial-deformdemo (it never worked)

* removed six; reactivated validation (do we still need it?)

* make isort happy

* update python version in docs, setup.py; added me to contributors

* list specific python versions; update ci python setup

* fix multi select test

deformdemo/test.py

@@ -3358,7 +3358,7 @@ def test_submit_complex_interaction(self):
         seq_height = findcss(".deform-seq-item").size["height"]
 
         persons = findxpaths(
-            '//div[@class="panel-heading"][contains(text(), "Person")]'
+            '//div[@class="card-header"][contains(text(), "Person")]'
         )
 
         # Move item 3 up two