Build both Qt4 and Qt5

.travis.yml

 language: cpp
+env:
+  - QT="-DWITH_QT4=0"
+  - QT="-DWITH_QT4=1"
 os:
   - linux
   - osx
 compiler:
   - gcc
   - clang
-script: mkdir build && cd build && cmake .. -DWITH_SERVER=1 && make
+script: mkdir build && cd build && cmake .. $QT -DWITH_SERVER=1 && make
 install: ./travis-dependencies.sh
 cache: apt

travis-dependencies.sh

@@ -2,8 +2,8 @@
 
 if [[ $TRAVIS_OS_NAME == "osx" ]] ; then
   brew update
-  brew install qt protobuf libgcrypt
+  brew install qt qt5 protobuf libgcrypt
 else
   sudo apt-get update -qq
-  sudo apt-get install -y qtmobility-dev libprotobuf-dev protobuf-compiler libqt4-dev
+  sudo apt-get install -y qtmobility-dev libprotobuf-dev protobuf-compiler libqt4-dev qt5-default qttools5-dev-tools
 fi