Require GCC 4.9

A compiler with good enough C++11 support is required to build ycmd.

.travis.yml

@@ -34,7 +34,9 @@ addons:
     packages:
      - cmake-data
      - cmake
-     - g++-4.8
+     # 4.9 is the first version of GCC with good enough C++11 support to build
+     # ycmd.
+     - g++-4.9
      - ninja-build
      # Everything below is a Python build dep (though it depends on Python
      # version). We need them because pyenv builds Python.

ci/travis/travis_install.linux.sh

@@ -5,8 +5,8 @@
 
 mkdir ${HOME}/bin
 
-ln -s /usr/bin/g++-4.8 ${HOME}/bin/c++
-ln -s /usr/bin/gcc-4.8 ${HOME}/bin/cc
+ln -s /usr/bin/g++-4.9 ${HOME}/bin/c++
+ln -s /usr/bin/gcc-4.9 ${HOME}/bin/cc
 
 export PATH=${HOME}/bin:${PATH}