sadb.execAdbShellCommand(args) not working

I got the following error when trying to use the shutdown() method:

```
Error Occurred! TypeError: this.execShellAdbCommand is not a function
    at SimpleADB.shutdown (/home/andrewk/projects/FHD-100/nodejs/node_modules/simple-adb/build/SimpleADB.js:266:25)
```

It appears that execShellAdbCommand isn't in the code anywhere. 