u3d returns code=0 if failed

[alexander-ossur]

Issue Checklist

• I'm using the latest u3d version
• I ran u3d --help
• I read the README
• I made sure that a similar issue doesn't exit

Issue Description

While "u3d install [any invalid version]" returns error message, it does not set return code to "1". In case of automated deployment there is no way to tell if that command succeeded of failed.

Good to mention though "u3d -- -batchmode [and etc]" forwards Unity's return code successfully