language: node_js
node_js:
  - "12"
  - "11"
  - "10"
  - "9"
  - "8"
  - "7"
  - "6"

language: node_js
node_js:
  - "13"
  - "12"
  - "11"
  - "10"
  - "9"
  - "8"

Remove Node 6 and 7 from Travis CI rotation, and add 13.
Remove Node 6 and 7 from Travis CI rotation, and add 13.

The latest version of Meteor (1.9) uses Node 12, and the previous several
versions use Node 8, so Node 6 and 7 are no longer relevant.
