Update .travis.yml

.travis.yml

@@ -4,12 +4,14 @@ python:
 install:
   - pip install -r requirements.txt
   - pip install lxml --upgrade
+  - pip install http://xmlsoft.org/sources/python/libxml2-python-2.6.21.tar.gz
   - pip install PyXmlSec --allow-external PyXMLSec --allow-insecure PyXMLSec
   - pip install coveralls
 script: 
   coverage run --source=pytrustnfe setup.py nosetests
 before_install:
   - sudo apt-get update -qq
+  - sudo apt-get upgrade python-pip
   - sudo apt-get install -qq libxml2-dev libxmlsec1-dev libxslt-dev 
   - sudo apt-get install -qq python-dev python-lxml python-libxml2
   - sudo apt-get install -qq python-libxslt1 libxml2