Update test scheme

Author: ShangtongZhang

.travis.yml

@@ -1,7 +1,6 @@
 language: python
 python:
-  - "2.7"
-  - "3.5"
+  - "3.6"
 install:
   - pip install tox tox-travis
 script:

chapter01/__init__.py

@@ -99,42 +99,3 @@ def figure_4_1():
 
 if __name__ == '__main__':
     figure_4_1()
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