Fix for "could not create work tree dir" during project creation on Windows machines

This is a fix for the 
```
fatal: could not create work tree dir 'C:\Users\Administrator\.config\roots\templates\default'.:No such file or directory
``` 
error message that users receive upon trying to create a new roots project on Windows machines.
The problem stems from a git issue and isn't present on other OSs.

Windows also has trouble with the `shell.exec` method using `;` to separate commands. That has been remedied in the `new` command also. 

I also fixed a few semicolon errors I saw with my linter. 

And last, but not least, I saw that [this](https://github.com/snowe2010/roots/blob/5079401595636304c5288c7e3057d8a0f0332f78/lib/commands/new.js#L84) line of code will never be hit, but I wasn't sure what to do about it.