Specified exact versions of packages to fix travis build issue

.travis.yml

@@ -9,7 +9,7 @@ cache:
 before_install:
     - sudo apt-get update
     - sudo apt-get install --no-install-recommends -y libsdl1.2debian python3-pip
-    - sudo pip3 install pylint pycodestyle
+    - sudo pip3 install -r requirements.txt
 
 install:
     - tests/install_blender.sh

requirements.txt

@@ -0,0 +1,3 @@
+# Python requirements for development
+pylint==1.9.2
+pycodestyle==2.4.0