[ci] Adds python3 in travis

.travis.yml

@@ -1,6 +1,7 @@
 language: python
 python:
   - "2.7"
+  - "3.6"
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
 install: 
  - pip install requests

CHANGELOG.md

@@ -1,5 +1,10 @@
 This file will only list released and supported versions, usually skipping over very minor updates.
 
+Unreleased
+==========
+
+* Python 3 upgrade
+
 3.0.0
 =====