Update .travis.yml

.travis.yml

@@ -3,6 +3,14 @@ node_js:
   - "7.3.0"
 before_script:
   - "mkdir -p ./.config && cp ./.ci-files/config.yml ./.config"
+env:
+  - CXX=g++-4.8
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-4.8
 cache:
   directories:
     - node_modules