chore: make travis be able to build native addons

Author: dignifiedquire

.travis.yml

@@ -14,12 +14,21 @@ script:
   - npm test
   - npm run coverage
 
-addons:
-  firefox: 'latest'
 
 before_script:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
 
 after_success:
   - npm run coverage-publish
+
+env:
+  - CXX=g++-4.8
+
+addons:
+  firefox: 'latest'
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-4.8