use gcc 4.8 on travis

.travis.yml

@@ -17,7 +17,9 @@ addons:
     build_command: make
     branch_pattern: coverity_scan
 before_install:
+   - sudo add-apt-repository ppa:ubuntu-toolchain-r/test
    - sudo apt-get update -qq
+   - sudo apt-get install -qq gcc-4.8
    - sudo apt-get install -qq --no-install-recommends build-essential cmake python-lxml graphviz doxygen wget
    - wget http://security.ubuntu.com/ubuntu/pool/main/c/check/check_0.9.10-6ubuntu3_amd64.deb
    - sudo dpkg -i check_0.9.10-6ubuntu3_amd64.deb