ci: test in lowest suported node version

Author: gr2m

.travis.yml

@@ -5,7 +5,7 @@ services:
 
 node_js:
   - 10
-  - 8
+  - 8.3 # minimal supported node version
 
 # Trigger a push build on master and greenkeeper branches + PRs build on every branches
 # Avoid double build on PRs (See https://github.com/travis-ci/travis-ci/issues/1147)