Remove #shellescape from block fed destination param

When providing a destination platform and/or name that contains a space, the added #shellescape to the string causes the concatenation to look like so:
```
-destination platform='iOS\ Simulator',name='iPad\ Retina'
```
This only is an issue with params fed through a block. The single quotes already take care of the spaces, and the extra escaping causes an error. The #shellescape is appropriate when the destination param is fed a string though (as opposed to a block). 

Tests updated too. 

Great project btw. It's a pain writing all of this stuff out normally.