Add missing package gettext for Travis CI

Author: flashcode

.travis.yml

@@ -6,7 +6,7 @@ python:
 
 before_install:
   - sudo apt-get update -qq
-  - sudo apt-get install -y aspell aspell-fr libenchant-dev
+  - sudo apt-get install -y gettext aspell aspell-fr libenchant-dev
 
 install:
   - "pip install pylint"