chore: add updated compiler for Travis

Author: wesleycho

.travis.yml

@@ -1,6 +1,14 @@
 language: node_js
 node_js:
   - "5.2"
+env:
+  - CXX=g++-4.8
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-4.8
 
 before_install:
   - export DISPLAY=:99.0