travis-remote-shell fails for OSX builds

Got the following when trying to debug tests on OSX:

```
$ eval "$(curl -sL https://raw.github.com/fniephaus/travis-remote-shell/master/run.sh)"
--2015-11-24 17:20:59-- https://dl.ngrok.com/ngrok_2.0.19_linux_amd64.zip
Resolving dl.ngrok.com... 198.58.107.51
Connecting to dl.ngrok.com|198.58.107.51|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 4021793 (3.8M) [application/zip]
Saving to: 'ngrok.zip'
ngrok.zip 100%[=====================>] 3.83M 13.3MB/s in 0.3s
2015-11-24 17:21:00 (13.3 MB/s) - 'ngrok.zip' saved [4021793/4021793]
Archive: ngrok.zip
inflating: ngrok
nc: illegal option -- e
usage: nc [-46AacCDdEFhklMnOortUuvz] [-K tc] [-b boundif] [-i interval] [-p source_port]
[-s source_ip_address] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]
/Users/travis/build.sh: line 54: ./ngrok: cannot execute binary file
No matching processes belonging to you were found
```

Thanks for the great project!