Update CI test to LTS version

abetomo · abetomo · commit fae907f2d752 · 2018-09-07T20:30:54.000+09:00
https://github.com/nodejs/Release#release-schedule
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,5 @@
 language: node_js
 node_js:
-  - "4"
   - "6"
-  - "7"
+  - "8"
+  - "10"
