Add compiler to Travis config

Author: andru

.travis.yml

@@ -1,4 +1,12 @@
 language: node_js
 sudo: false
 node_js:
-  - "5.3.0"
+  - "4"
+env:
+  - CXX=g++-4.8
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-4.8