Add ubuntu-toolchain to travis. Latest GCC supported version is 4.9.

.travis.yml

@@ -9,16 +9,18 @@ node_js:
   - "0.10"
 addons:
   apt:
+    sources:
+      - ubuntu-toolchain-r-test
     packages:
-    - libzmq3-dev
-    - libprotobuf-dev
-    - graphicsmagick
-    - rethinkdb
-    - g++-5.2
-    - yasm
+      - libzmq3-dev
+      - libprotobuf-dev
+      - graphicsmagick
+      - rethinkdb
+      - g++-4.9
+      - yasm
 before_install:
-    - if [ "${TRAVIS_OS_NAME}" == "linux" ]; then export CXX=g++-5.2; fi
-    - if [ "${TRAVIS_OS_NAME}" == "osx" ]; then brew install yasm; fi
+  - if [ "${TRAVIS_OS_NAME}" == "linux" ]; then export CXX=g++-4.9; fi
+  - if [ "${TRAVIS_OS_NAME}" == "osx" ]; then brew install yasm; fi
 script:
   - gulp build
 before_script: