Ensure Trireme is detected as node and not Rhino

Trireme emulates a Node environment on Rhino.  When in use, it is
desirable that it is detected as node, not Rhino.

This commit changes the order in which Rhino/node is detected, detecting
node first, which ensures that Trireme is detected as node.
Merge pull request #630 from jroper/support-trireme

Don't detect Trireme as Rhino