Trying fix travis 7. Add apt-get update

Author: pitbulk

.travis.yml

@@ -3,6 +3,7 @@ python:
   - '2.7'
 
 install:
+  - sudo apt-get update -qq
   - sudo apt-get install -qq python-dev libxml2-dev libxmlsec1-dev
   - 'travis_retry pip install .'
   - 'travis_retry pip install -e ".[test]"'