update Linux Travis CI to Qt 5.9.7

.travis_linux.sh

@@ -10,7 +10,7 @@ fi
 
 # Install qt5.9
 sudo add-apt-repository ppa:george-edison55/cmake-3.x -y
-sudo add-apt-repository ppa:beineri/opt-qt596-trusty -y
+sudo add-apt-repository ppa:beineri/opt-qt597-trusty -y
 sudo apt-get update -qq
 sudo apt-get -y install qt59base qt59webengine qt59webchannel qt59svg qt59location qt59tools qt59translations
 source /opt/qt*/bin/qt*-env.sh