[travis] Quote requirement

.travis.yml

@@ -16,7 +16,7 @@ before_install:
 - sudo add-apt-repository -y ppa:biometrics/bob
 - sudo apt-get update -qq
 - sudo apt-get install -qq --force-yes libboost-all-dev libblitz1-dev libatlas-dev libatlas-base-dev liblapack-dev libhdf5-serial-dev texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended gfortran
-- pip install --find-links https://www.idiap.ch/software/bob/wheels/travis/ --use-wheel sphinx<1.3.4 nose numpy scipy matplotlib coverage cpp-coveralls
+- pip install --find-links https://www.idiap.ch/software/bob/wheels/travis/ --use-wheel 'sphinx<1.3.4' nose numpy scipy matplotlib coverage cpp-coveralls
 - pip install --find-links https://www.idiap.ch/software/bob/wheels/travis/ --use-wheel --pre -r requirements.txt coveralls
 install:
 - python bootstrap-buildout.py