Update boost in travis-ci to fix build failure

CI/before_install.linux.sh

@@ -10,9 +10,10 @@ fi
 
 echo "yes" | sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu `lsb_release -sc` main universe restricted multiverse"
 echo "yes" | sudo apt-add-repository ppa:openmw/openmw
+echo "yes" | sudo apt-add-repository ppa:boost-latest/ppa
 sudo apt-get update -qq
 sudo apt-get install -qq libgtest-dev google-mock
-sudo apt-get install -qq libboost-filesystem-dev libboost-program-options-dev libboost-system-dev libboost-thread-dev
+sudo apt-get install -qq libboost-filesystem1.55-dev libboost-program-options1.55-dev libboost-system1.55-dev libboost-thread1.55-dev
 sudo apt-get install -qq libavcodec-dev libavformat-dev libavutil-dev libswscale-dev libavresample-dev
 sudo apt-get install -qq libbullet-dev libopenscenegraph-dev libmygui-dev libsdl2-dev libunshield-dev libtinyxml-dev libopenal-dev libqt4-dev
 sudo apt-get install -qq cmake-data #workaround for broken osgqt cmake script in ubuntu 12.04