also install g++ 4.9.

.travis.yml

@@ -2,7 +2,7 @@ before_install:
     - sudo apt-add-repository -y ppa:ondrej/php5
     - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
     - sudo apt-get update
-    - sudo apt-get install -qq libsqlite3-dev libcurl4-openssl-dev libxml2-dev libstfl-dev libjson-c-dev libncursesw5-dev bc gcc-4.9
+    - sudo apt-get install -qq libsqlite3-dev libcurl4-openssl-dev libxml2-dev libstfl-dev libjson-c-dev libncursesw5-dev bc gcc-4.9 g++-4.9
     - sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 50
     - sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.9 50
 language: cpp