[travis] Add node 12 and remove node 6

Author: lpinca

.travis.yml

@@ -3,13 +3,13 @@ language: node_js
 matrix:
   fast_finish: true
   include:
+    - node_js: "12"
+      env: SCRIPT=test
     - node_js: "10"
       env: SCRIPT=test
     - node_js: "8"
       env: SCRIPT=test
-    - node_js: "6"
-      env: SCRIPT=test
-    - node_js: "8"
+    - node_js: "10"
       env:
         - secure: IF01oyIKSs0C5dARdYRTilKnU1TG4zenjjEPClkQxAWIpUOxl9xcNJWDVEOPxJ/4pVt+pozyT80Rp7efh6ZiREJIQI1tUboBKSqZzSbnD5uViQNSbQ90PaDP0FIUc0IQ5o07W36rijBB0DTmtU1VofzN9PKkJO7XiSSXevI8RcM=
         - SAUCE_USERNAME=url-parse