Install script fails on Linux

https://raw.githubusercontent.com/nerves-hub/nerves_hub_cli/master/install.sh

Following installation instructions:
```sh

$ curl --proto '=https' --tlsv1.2 -fsSL https://raw.githubusercontent.com/nerves-hub/nerves_hub_cli/master/install.sh | sh
sh: 31: [[: not found
sh: 37: [[: not found
sh: 7: [[: not found
sh: 16: [[: not found

gzip: stdin: not in gzip format
tar: Child died with signal 13
tar: Error is not recoverable: exiting now
```