Ensured that Travis uses latest versions of dependencies (closes snowplow#149)

Author: fblundun

.travis.yml

@@ -9,12 +9,10 @@ python:
   - "3.3"
 # command to install dependencies
 install:
-  - "pip install python-dateutil"
   - "pip install httmock"
   - "pip install freezegun"
-  - "pip install nose"
   - "pip install coveralls"
-  - "pip install -r requirements.txt"
+  - "python setup.py install"
 # command to run tests
 script:
   nosetests --with-coverage --cover-package=snowplow_tracker