Cart link code updated

I used this code 
```
<?php echo get_permalink($edd_options['purchase_page']); ?>
```
in my theme and it didn't work .

after a little headache and research I found out
```
 <?php echo edd_get_checkout_uri(); ?> 
```
so, for new developers the starter theme should portray the best and error free options.
Merge pull request #11 from ahmadawais/patch-2

Cart link code updated