Stop testing against inactive LTS releases of node

Author: consideRatio

.travis.yml

@@ -3,11 +3,11 @@ sudo: false
 branches:
   except:
     - /^greenkeeper.*/
+# Test against Long Term Support (LTS) releases in a "current", "active", and
+# "maintenance" status: https://nodejs.org/en/about/releases/
 node_js:
   - 12
   - 10
-  - 8
-  - 6
 install:
   - npm install -g codecov
   - npm install