[weblate] Fix python-future tag

manifests/weblate/python_modules.pp

@@ -82,6 +82,7 @@ class tails::weblate::python_modules () {
 
   tails::pip_package_from_repo { 'future':
     version => '0.18.2',  # >=0.18.0
+    tag     => 'v0.18.2',
     url     => 'https://github.com/PythonCharmers/python-future',
   }