Use correct compiler to build glbinding on Travis

cmake/travis_install_linux.sh

 
 if [ "$CXX" = "clang++" ]; then sudo apt-get install --allow-unauthenticated clang-3.5; fi
 
-git clone https://github.com/hpicgs/glbinding.git
-cd glbinding
-cmake .
-make -j4
-sudo make install
-cd ..
-

cmake/travis_script_linux.sh

 
 if [ "$CXX" = "clang++" ]; then export CXX="clang++-3.5"; fi
 
+git clone https://github.com/hpicgs/glbinding.git
+cd glbinding
+cmake .
+make -j4
+sudo make install
+cd ..
+
 mkdir build && cd build && cmake .. && make -j 4 && make check