luaver should not be executable (reversing #34)

[umireon]

Making ./luaver executable (#34), which was my PR, revealed to cause various problems.

First, that change shows the help text unexpectedly, for instance: https://travis-ci.org/DhavalKapil/luaver/jobs/264895203#L412

Second, combined commands like . /path/to/luaver && luaver install does not works in expected way. https://github.com/Homebrew/homebrew-core/pull/16839#issuecomment-322604541

Solving these problems are hard because there are no easy ways to tell if the script was sourced or directly-executed.

In conclusion, I apologize for my carelessness and my fault, 🙇 but #34 should be reversed 😿. Since ./luaver should not be directly-executed, executable permission flag should also be dropped.