Can't read password when Alpaca is launched through Windows Git Bash

[samuong]

Steps to reproduce:

1. On a Windows machine, open up Git Bash
2. Launch Alpaca using /path/to/alpaca -d mydomain

Expected behaviour:

Alpaca should prompt for the user's password and use that to authenticate to the proxy.

Actual behaviour:

The password prompt is printed, followed by an error message:

main.go:52: Error reading password from stdin: The handle is invalid.

Workaround:

Run Alpaca from a Command Prompt (cmd.exe) window.

[samuong]

This could be related to golang/go#11914