fix: Fix the native extension for OSX

Requiring the .so file doesn't work on OSX, apparently (see #12),
so `Rutie.init` *is* necessary (danielpclark/rutie#142).

Is the following documentation is Linux specific?
https://docs.ruby-lang.org/en/3.0/extension_rdoc.html

Anyway, since we use Thermite we need to resolve the extension at
`lib/tantiny.so`, hence `lib_path` and `lib_prefix` options.

lib/tantiny.rb

@@ -15,7 +15,6 @@
 require "tantiny/query"
 require "tantiny/index"
 
-require_relative "tantiny.so"
-
 module Tantiny
+  Rutie.new(:tantiny, lib_path: __dir__, lib_prefix: "").init("Init_tantiny", __dir__)
 end