Instruct travis to install six.

.travis.yml

@@ -10,9 +10,10 @@ python:
 before_install:
   - sudo apt-get install -qq libatlas3gf-base libatlas-dev
 install:
-#If we don't install numpy before SciPy 0.10.1, the SciPy installations fails.
+# If we don't install numpy before SciPy 0.10.1, the SciPy installations fails.
+  - "pip install -q six==1.2.0 --use-mirrors"
   - "pip install -q numpy==1.5 --use-mirrors"
-#We can't install SciPy as there is no BLAS installed.
+# We can't install SciPy as there is no BLAS installed.
   - "pip install . --no-deps --use-mirrors"
 # command to run tests
 env: