Tell travis to use updated version of gcc

.travis.yml

@@ -4,8 +4,12 @@ before_install:
     # Setup virtual x server for gui testing
     - export DISPLAY=:99.0
     - sh -e /etc/init.d/xvfb start
-    # Install dependencies
+    
+    # Upgrade gcc
     - sudo apt-get update -qq
+    - sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 90
+    
+    # Install dependencies
     - sudo apt-get install -qq libwxgtk3.0-dev libwxgtk3.0-0 libssh2-1-dev
 
 # Build with both gcc and clang