Test on more recent Node 8.

RubenVerborgh · RubenVerborgh · commit 0b7a027ccb9e · 2018-05-02T13:54:37.000-04:00
Avoids an npm bug in an earlier version.
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,7 @@
 sudo: false
 language: node_js
 node_js:
-  - "8.0"
+  - "8.10"
   - "10.0"
   - "node"
 env:
