Add ppa to get Octave 4.0 in Trusty

It is necessary for using the latest mex-based Octave bindings

.ci/travis-deps.sh

@@ -4,6 +4,7 @@ set -e
 
 #if OS is linux or is not set
 if [ "$TRAVIS_OS_NAME" = linux -o -z "$TRAVIS_OS_NAME" ]; then
+    sudo add-apt-repository ppa:octave/stable -y
     sudo sh -c 'echo "deb http://www.icub.org/ubuntu trusty contrib/science" > /etc/apt/sources.list.d/icub.list'
     sudo apt-get update
     sudo apt-get -y --force-yes install -qq libboost-filesystem-dev libboost-system-dev libboost-thread-dev libtinyxml-dev libboost-iostreams-dev icub-common  valgrind liblua5.1-0-dev lua5.1 swig python-dev cmake libeigen3-dev liboctave-dev