[travis] Pip upgrade before installing other wheels

.travis.yml

@@ -15,6 +15,7 @@ before_install:
 - sudo apt-get update -qq
 - sudo apt-get install -qq --force-yes libjpeg8-dev libnetpbm10-dev libpng12-dev libtiff4-dev libgif-dev libboost-all-dev libblitz1-dev libhdf5-serial-dev libvl-dev dvipng texlive-latex-base texlive-latex-extra texlive-math-extra texlive-latex-recommended texlive-fonts-recommended libatlas-dev libatlas-base-dev liblapack-dev
 - sudo apt-get install -qq --force-yes python-opencv libcv-dev libcvaux-dev libopencv-dev
+- pip install --upgrade pip
 - pip install --upgrade --find-links https://www.idiap.ch/software/bob/wheels/travis/ --use-wheel sphinx nose numpy scipy matplotlib coverage
 - pip install --find-links https://www.idiap.ch/software/bob/wheels/travis/ --use-wheel --pre -r requirements.txt coveralls
 - pip install --find-links https://www.idiap.ch/software/bob/wheels/travis/ --use-wheel --pre -r databases.txt