Reduce gem package size

[pocke]

This pull request reduces the gem package size.

Currently this gem is 2.5MB.

$ cd path/to/installed/dir/lib/ruby/gems/2.7.0/gems
$ du mimemagic-0.3.5/ --summarize -h
2.5M    mimemagic-0.3.5/

But it contains unnecessary files for the package users, which are under tests/ and script/ directory.
Especially script/ directory is large, but it isn't necessary for the users.

So this pull request removes them from the package.
It reduces 2.3MB.

# after this pull request
$ cd path/to/installed/dir/lib/ruby/gems/2.7.0/gems
$ du mimemagic-0.3.5/ --summarize -h
184K    mimemagic-0.3.5/

[minad]

Is it a good idea to distribute gems without tests? Is this common practice? The gem us quite mature and no one complained before, so I don't see a pressing reason to change it.

[pocke]

It is a common practice because Bundler generates a gemspec with a similar setting.

https://github.com/rubygems/rubygems/blob/ff86ba494d54db5a9d52f13b1adf672e5669b010/bundler/lib/bundler/templates/newgem/newgem.gemspec.tt#L25-L29

In my case, I found some large packages when I'm trying to reduce build time on CircleCI for my Rails app.
I use a cache mechanism of CircleCI for bundler. https://circleci.com/docs/2.0/caching/#bundler-ruby
And restoring cache spends 20~30s on average, for 322MB cache. it is not fast and small enough, so I'd like to reduce the build time by reducing the package size.