Move underscore from "dependencies" to "devDependencies".

[bolinfest]

According to your package.json, this package has a dependency on underscore ~1.4.4, but looking through your lib/ directory, the only file that require()'s it is avltree.js, but I don't see it used in there.

It looks like it is used in your test directory, though, so I think you still need it in "devDependencies" (and would then have to remove _ = require('underscore') from avltree.js).