[CI] fix python3 configuration

which was broken since  bcf1007

Author: nim65s

.travis.yml

@@ -1,24 +1,25 @@
 language: cpp
 sudo: required
-compiler: 
+compiler:
 - clang
 - gcc
 env:
   global:
   - secure: "SnIBG/xLIHX3CSvUbqqsX8xTVqIqQ7fFS6HWO6KZQVBsT6yugTwYHbyhNiU531JejYJ/I3ZrDhXfYH3qFZiYxnH1sifvwV+fnTtMXpPN7qPZwIymkjcmm6gJF51e0C7VOfUbvKFv0ngwj+ul21rgZSMuoEvxPK0WxtE3/ZSfn9c="
-  - APT_DEPENDENCIES="doxygen doxygen-latex libboost-all-dev libeigen3-dev liblapack-dev libblas-dev gfortran python-dev python-sphinx"
+  - APT_DEPENDENCIES="doxygen doxygen-latex libboost-all-dev libeigen3-dev liblapack-dev libblas-dev gfortran python3-dev python3-sphinx"
   - DEBSIGN_KEYID=5AE5CD75
+  - CMAKE_ADDITIONAL_OPTIONS="-DPYTHON_EXECUTABLE=/usr/bin/python3"
 notifications:
   email:
   - hpp-source@laas.fr
 branches:
   only:
   - master
   - devel
-matrix: 
-  allow_failures: 
+matrix:
+  allow_failures:
   - compiler: clang
-before_install: ./travis_custom/custom_before_install  
+before_install: ./travis_custom/custom_before_install
 script:
   - sudo free -m -t
   - ./.travis/run ../travis_custom/custom_build