Chore - Remove Node v7 from CI, only keep LTS versions and Node v9. (#370)

* chore(.travis.yml) node 7 removed from CI, yaml indented

* chore(.travis.yml) run CI only on node LTS versions

* chore(.travis) node v9 added

* chore(.travis) node v4 removed

.travis.yml

@@ -1,13 +1,11 @@
 language: node_js
 sudo: false
 node_js:
-- '4'
-- '6'
-- '7'
-- '8'
-- '9'
+  - 6
+  - 8
+  - 9
 script:
-- npm run ci
+  - npm run ci
 env:
   global:
-  - secure: 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
+    - secure: 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