add C++11 compiler to travis

.travis.yml

@@ -4,13 +4,15 @@ node_js:
 sudo: false
 addons:
   apt:
+    sources:
+    - ubuntu-toolchain-r-test
     packages:
     - libcairo2-dev
     - libjpeg8-dev
     - libpango1.0-dev
     - libgif-dev
     - build-essential
-    - g++
+    - g++-4.8
 script:
   - npm run-script test-travis
 notifications:
@@ -18,7 +20,8 @@ notifications:
     channels:
       - irc.esper.net#crafatar
     skip_join: true
-env: TRAVIS=true
+env:
+  - TRAVIS=true CXX=g++-4.8
 services:
   - redis-server
 cache: