Cleanup CI configuration (#945)

* Cleanup CI configuration

- Python 3.8 is now official
- Django 3.0rc1 is now available
- Cleanup indent in tox.ini

* Update tox.ini

.travis.yml

@@ -1,14 +1,10 @@
-sudo: false
-
-
-dist: xenial
 language: python
 python:
   - "2.7"
   - "3.5"
   - "3.6"
   - "3.7"
-  - "3.8-dev"
+  - "3.8"
 
 cache: pip
 

tox.ini

@@ -1,24 +1,24 @@
 [tox]
 envlist =
-       {py27,py35,py36}-django111,
-       {py35,py36}-django20,
-       {py35,py36,py37,py38}-django21,
-       {py35,py36,py37,py38}-django22,
-       {py36,py37,py38}-django30,
-       {py36,py37,py38}-django-latest,
+    {py27,py35,py36}-django111,
+    {py35,py36}-django20,
+    {py35,py36,py37}-django21,
+    {py35,py36,py37,py38}-django22,
+    {py36,py37,py38}-django30,
+    {py36,py37,py38}-django-latest,
 
 [testenv]
 deps =
     django111: django>=1.11.0,<2.0
     django20: django>=2.0,<2.1
     django21: django>=2.1,<2.2
     django22: django>=2.2,<2.3
-    django30: django>=3.0a1,<3.1
+    django30: django>=3.0rc1,<3.1
     django-latest: https://github.com/django/django/archive/master.tar.gz
     -rrequirements.txt
 whitelist_externals = make
 commands = make test
 ignore_outcome =
     django-latest: True
 setenv =
-       PYTHONDONTWRITEBYTECODE=1
+    PYTHONDONTWRITEBYTECODE=1