Add Python 3.8 support and Django 2.1 to 3.0 testing

.travis.yml

@@ -7,10 +7,18 @@ templates:
     dist: xenial
     sudo: required
 
+  py38: &py38
+    python: 3.8
+    dist: xenial
+    sudo: required
+
   django1-9: &django1-9 DJANGO=1.9
   django1-10: &django1-10 DJANGO=1.10
   django1-11: &django1-11 DJANGO=1.11
   django2-0: &django2-0 DJANGO=2.0
+  django2-1: &django2-1 DJANGO=2.1
+  django2-2: &django2-2 DJANGO=2.2
+  django3-0: &django3-0 DJANGO=3.0
 
   postgres: &postgres DATABASE_URL='postgres://postgres@127.0.0.1/django_nece_test'
 
@@ -39,7 +47,12 @@ matrix:
   - { <<: *py37, env: [*django1-10, *postgres]}
   - { <<: *py37, env: [*django1-11, *postgres]}
   - { <<: *py37, env: [*django2-0, *postgres]}
+  - { <<: *py37, env: [*django2-1, *postgres]}
+  - { <<: *py37, env: [*django2-2, *postgres]}
+  - { <<: *py37, env: [*django3-0, *postgres]}
 
+  - { <<: *py38, env: [*django2-2, *postgres]}
+  - { <<: *py38, env: [*django3-0, *postgres]}
 
 script:
 - python setup.py build_ext -i

nece/managers.py

@@ -79,7 +79,7 @@ def _clone(self, *args, **kwargs):
 
     def filter(self, *args, **kwargs):
         if not self.is_default_language(self._language_code):
-            for key, value in kwargs.items():
+            for key, value in list(kwargs.items()):
                 if key.split('__')[0] in self.model._meta.translatable_fields:
                     del kwargs[key]
                     key = 'translations__{}__{}'.format(

setup.py

@@ -44,6 +44,7 @@
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Topic :: Database",
         "Topic :: Internet :: WWW/HTTP :: Dynamic Content",
         "Topic :: Text Processing :: Linguistic",

tests/requirements/django-2.1.txt

@@ -0,0 +1,2 @@
+-r requirements_base.txt
+django>=2.1,<2.2

tests/requirements/django-2.2.txt

@@ -0,0 +1,2 @@
+-r requirements_base.txt
+django>=2.2,<3.0

tests/requirements/django-3.0.txt

@@ -0,0 +1,2 @@
+-r requirements_base.txt
+django>=3.0,<3.1

tests/requirements/requirements_base.txt

@@ -1,5 +1,5 @@
 django-admin-json-editor==0.2.0
-six==1.10.0
+six
 psycopg2
 dj-database-url
 coveralls