Fix urllib3 dependency for travis

Author: giorgiobasile

.travis.yml

@@ -10,7 +10,7 @@ install:
     - "pip3 install beautifulsoup4 Sickle validators"
     - "pip3 install requests-mock"
     - "pip3 install 'elasticsearch>=1.0.0,<2.0.0'"
-    - "pip3 install urlib3-mock"
+    - "pip3 install urllib3-mock"
 script:
     - python setup.py test
     - python setup.py sdist