Remove -e backup files created by sed on macOS about flutter-redux-starter

[danibjor]

starter.sh have a cleanup switch for cleaning up temp-files

[gentlefox]

On OSX sed -i expects a file extension.
Thus when sed -i -e "s/stub/$module/g" "$filename.dart" is called, it creates a backup using the next argument "-e".

The fix: sed -i '' -e "s/stub/$module/g" "$filename.dart" assigning an empty string as the extension parameter.

[hillelcoren]

I think I tried that, I believe adding '' causes problems on Windows or Linux

[gentlefox]

Yeah, I've been seeing that. The cleanup script is a nice workaround.

I've been working with the PR that Julian Paraian submitted, trying to get the shell scripting to be cross-platform. Progress would have been faster with the inclusion of code comments...

The amount of time I've been able to focus on it looks to be reduced for a while as it appears we have to stop using Flutter for the current project (for now) meaning the rush job of creating it anew in another format.

I'll still see what I can do towards contributing to the amazing work you're doing here - thank you for your contribution!