Fix travis ci build for nodejs 4+.

Author: marco.minetti

.travis.yml

@@ -1,10 +1,12 @@
 language: node_js
+env:
+  - CXX=g++-4.8
 addons:
   apt:
     sources:
-    - ubuntu-toolchain-r-test
+      - ubuntu-toolchain-r-test
     packages:
-    - gcc-4.8
+      - g++-4.8
 node_js:
  - "0.10"
  - "0.12"