Force travis to always use lxml from no binary

Author: pitbulk

.travis.yml

@@ -16,6 +16,7 @@ install:
   - sudo apt-get update -qq
   - sudo apt-get install -qq swig python-dev libxml2-dev libxmlsec1-dev
   - 'travis_retry pip install .'
+  - 'travis_retry pip install --force-reinstall --no-binary lxml lxml'
   - 'travis_retry pip install -e ".[test]"'
 
 script: