Expand test matrix

Author: atodorov

.travis.yml

@@ -5,11 +5,15 @@ python:
   - "3.6"
 env:
   - PYLINT=1.9.2
-  - PYLINT=github
+  - PYLINT=1.9.3
+  - PYLINT=2.0.0
+  - PYLINT=2.1.1
+  - PYLINT=2.2.2
+  - PYLINT=master
 install:
   - |
     pip install coverage coveralls
-    if [ "$PYLINT" == "github" ]; then
+    if [ "$PYLINT" == "master" ]; then
         pip install https://github.com/PyCQA/astroid/zipball/master
         pip install https://github.com/PyCQA/pylint/zipball/master
     else