Updated minimal version of node because ns-cli requires node v8

reinaldorauch · reinaldorauch · commit 15247ca218c4 · 2018-10-30T16:33:46.000-03:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,6 @@
 language: node_js
 node_js:
-- '6'
+- '8'
 git:
   submodules: false
 before_script:
