Move dev dependencies to a rrequirements-dev file and fix the version

requirements-dev.txt

+mock==4.0.3
+unittest2==1.1.0
+pytest==6.2.5
+pytest-cov==3.0.0
+pytest-recording==0.12.0
+factory_boy==3.2.1

tox.ini

 [tox]
 envlist =
-  pep8
+  pep8,
   clean,
   py38,
 
 [testenv]
+basepython =
+    python3.8
+
 commands = pytest --cov odoo_somconnexio_python_client/
 deps =
-    mock
-    unittest2
-    pytest
-    pytest-cov
-    pytest-recording
-    factory_boy
+    -rrequirements-dev.txt
 
 setenv =
     ODOO_BASEURL=http://odoo-sc.local:8069
     ODOO_APIKEY=5b512e2f-1b02-4fdf-b49d-4dddf68b3002
 
-
 [testenv:clean]
 deps = coverage
 skip_install = true
@@ -39,9 +36,6 @@ commands = python setup.py sdist
 # Lint
 # --------------------------------------------------------------------
 [testenv:pep8]
-basepython =
-    python3.8
-
 deps =
     flake8
     flake8-quotes