pass rustup-setup.sh arguments to rustup-setup

this would let us call

```
curl https://sh.rustup.rs -sSf | sh -s -- -y
```

to install rustup without prompting.

closes #297

Author: Jorge Aparicio

rustup-setup.sh

@@ -56,7 +56,7 @@ main() {
         err "/dev/tty does not exist"
     fi
 
-    run "$_file" < /dev/tty
+    run "$_file" "$@" < /dev/tty
 
     local _retval=$?