Use node 6 and 8 in tests instead of 4 and 5

Eva Sarafianou · Eva Sarafianou · commit 07e38e74d3db · 2019-01-25T08:53:04.000-08:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,7 @@
 language: node_js
 node_js:
-  - "4"
-  - "5"
+  - "6"
+  - "8"
 env:
   - CXX=g++-4.8
 addons:
