Use dd instead of authopen to write file.
Use dd instead of authopen to write file.

Since runas already supports running command as administrator, we don't
need to use authopen anymore, also authopen requires extra operations to
set the correct application name, while runas just shows the right one.

Fixes https://github.com/atom/node-runas/issues/4.

atom/node-pathwatcher,mojodna/node-pathwatcher,mojodna/node-pathwatcher,leipert/node-pathwatcher-without-runas,leipert/node-pathwatcher-without-runas,dbkaplun/node-pathwatcher,dbkaplun/node-pathwatcher,dbkaplun/node-pathwatcher,ficristo/node-pathwatcher,ficristo/node-pathwatcher,meteor/node-pathwatcher,leipert/node-pathwatcher-without-runas,mojodna/node-pathwatcher,atom/node-pathwatcher,meteor/node-pathwatcher