Add python3.8 + isort + flake8

.travis.yml

@@ -5,11 +5,15 @@ python:
   - "3.6-dev"  # 3.6 development branch
   - "3.7"
   - "3.7-dev"  # 3.7 development branch
+  - "3.8"
+  - "3.8-dev"  # 3.8 development branch
+
 # command to install dependencies
 install:
   - pip install -U pip wheel setuptools
   - pip install -r requirements.txt
   - pip install -e .
+
 # command to run tests
 script:
   - isort -c --skip-glob=venv

requirements.txt

@@ -1,2 +1,4 @@
 dnspython==1.16.0
 idna==2.8
+isort==4.3.21
+flake8==3.7.8