update flake8 config and add django 2 to travis matrix

Author: Matthew Egan

.travis.yml

@@ -8,6 +8,7 @@ env:
     - DJANGO_VERSION=1.9
     - DJANGO_VERSION=1.10
     - DJANGO_VERSION=1.11
+    - DJANGO_VERSION=2.0
 
 install:
 - pip install -r requirements.txt

setup.cfg

@@ -1,3 +1,3 @@
 [flake8]
-max-line-length=79
+max-line-length=120
 exclude=migrations