`spawn` handles ENOTDIR differently based on ENV

spawn-ENOTDIR-different-results-based-on-env.js

osx =>
```js
cdieringer@Snapper-osx:~/node/coinstac-common$ node -v
v4.2.4
cdieringer@Snapper-osx:~/node/coinstac-common$ node debug test/
< Debugger listening on port 5858
...
break in src/models/computation/command.js:35
 33         cmd = spawn(this.cmd, this.args, { cwd: this.cwd });
 34     } catch (err) {
>35         debugger 
 36         return cb(err); // <== 'Error: spawn ENOTDIR'
 37     }
debug>
```

linux (codeship box) =>
```js
rof@railsonfire_db59a440-b8f9-0133-c46f-360779539cf5_4b897b15371a:~/clone$ node -v
v4.2.4
< Debugger listening on port 5858
debug> . ok
...
break in src/models/computation/command.js:41
 39     let errMsg = '';
 40     cmd.on('error', function(err) {
>41         debugger
 42         return cb(err); // <== 'Error: spawn ENOTDIR'
 43     })
```