Be more specific about the node version used for Travis
Be more specific about the node version used for Travis

Sometimes Travis fails because `nvm` would not be able to reach the node package with:

> Failed to install 12. Remote repository may not be reachable.

Perhaps being more specific will help with timing of node releases or more likely hitting the cache.

KWierso/treeherder,KWierso/treeherder,KWierso/treeherder,KWierso/treeherder