Add warning to CLI when running encrypt-file on Windows

[tdmalone]

Due to #4746, travis encrypt-file does not work on Windows. But, there's no indication that it doesn't work. It appears to work, but an encrypted file fails to unencrypt when the build is running, which can result in hours of debugging.

travis encrypt-file works fine on non-Windows machines.

Could a warning be added to the Travis CLI, when running encrypt-file on Windows, either stating that it is unsupported or is known to not work?

[stale]

Thanks for contributing to this issue. As it has been 90 days since the last activity, we are automatically closing the issue. This is often because the request was already solved in some way and it just wasn't updated or it's no longer applicable. If that's not the case, please do feel free to either reopen this issue or open a new one. We'll gladly take a look again! You can read more here: https://blog.travis-ci.com/2018-03-09-closing-old-issues

[tdmalone]

unstale pls :)

[stale]

Thanks for contributing to this issue. As it has been 90 days since the last activity, we are automatically closing the issue in 24 hours. This is often because the request was already solved in some way and it just wasn't updated or it's no longer applicable. If that's not the case, please do feel free to either reopen this issue or open a new one. We'll gladly take a look again! You can read more here: https://blog.travis-ci.com/2018-03-09-closing-old-issues

[tdmalone]

unstale

[stale]

Thanks for contributing to this issue. As it has been 90 days since the last activity, we are automatically closing the issue in 7 days. This is often because the request was already solved in some way and it just wasn't updated or it's no longer applicable. If that's not the case, please respond before the issue is closed, or open a new one after. We'll gladly take a look again! You can read more here: https://blog.travis-ci.com/2018-03-09-closing-old-issues

[tdmalone]

See also: #8777
Please unlock #4746