core: add pylint check of doc/docgen.py (Travis)

.travis.yml

@@ -5,7 +5,7 @@ before_script:
     - sudo apt-get update -qq
     - sudo apt-get -y install devscripts equivs python-pip libenchant-dev
     - sudo mk-build-deps -i debian/control
-    - sudo pip install msgcheck
+    - sudo pip install msgcheck pylint
 
 script:
     - mkdir build
@@ -15,6 +15,7 @@ script:
     - sudo make install
     - cd ..
     - msgcheck po/*.po
+    - pylint doc/docgen.py
 
 after_success:
     - weechat --help