Modified app/_Gruntfile to make the createLinuxApp step copy over the ic...

This is a proposed fix for issue 57, 'issue when running dist application on ubuntu 64'

I receive a similar error after running 'grunt dist-linux' and trying to start the application:

$ ./node-webkit app.nw/
[7651:1228/204657:FATAL:content_main_runner.cc(751)] Check failed: base::i18n::InitializeICU(). 
fish: Job 1, “./node-webkit app.nw/” terminated by signal SIGABRT (Abort)

The error signature is a little different than what was reported in the issue, but the main problem is the same: the icudtl.dat file is not being copied over from resources/node-webkit/Linux64/ to the dist/Linux64 folder.  If the file is copied over, the application will launch as expected.

This pull request makes a simple change in the Gruntfile so that the icudtl.dat is copied over every time that 'grunt dist-linux' is run.