Fix 'root' deprecation warning
Fix 'root' deprecation warning

This would previously be printed in part of the test log:

    (node:1628) [DEP0016] DeprecationWarning: 'root' is deprecated, use 'global'

Apparently, the global object was once called root, and this assignment
didn't have a `var`, so it was actually setting the global object.

I do wonder why that didn't break anything, but this is clearly what was
intended.

sidorares/node-x11,sidorares/node-x11,sidorares/node-x11