Upgrade dependencies, expand tests, fix formating, and bump to v1.0.2

[theycallmeswift]

This pull request cleans up the code base and updates the dependencies to the latest versions. Here's a list of what's included:

• Upgrade RSpec and Child Process to latest versions
• Add a default Rake task to run tests
• Migrate all tabs to spaces
• Restructure version so it can be imported into gemspec
• Reformat gemspec to be more readable and future-proof
• Expand test based on some common cases from jruby-sandbox

[ukutaht]

Thanks :+1: