Make build-v1.sh executable

I'm embarrassed to admit how long it took me to realize that the somewhat cryptic error I was getting:
```
events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: spawn EACCES
    at errnoException (child_process.js:980:11)
    at Process.ChildProcess._handle.onexit (child_process.js:771:34)
```
...was simply due to this file not being executable :see_no_evil: