travis: use default python version

Part of #20

Author: ligurio

.travis.yml

@@ -1,5 +1,13 @@
 language: python
-python: 2.7
+
+python:
+  - "2.7"
+  - "3.4"
+  - "3.5"
+  - "3.6"
+  - "3.7"
+  - "3.8"
+  - "3.8-dev"
 
 before_install:
   - sudo apt update -y

Makefile

@@ -5,7 +5,7 @@ default:
 lint: flake8 luacheck
 
 flake8:
-	python2 -m flake8 *.py lib/*.py
+	python -m flake8 *.py lib/*.py
 
 luacheck:
 	luacheck --config .luacheckrc .