avoid duplicate require due to symlinks
avoid duplicate require due to symlinks

When the centurion gem is installed under a symlinked directory, a simple `require 'centurion'` will error due to some files being loaded twice. Centurion requires some of its own files twice, once via `require <path>` and once again via `require_relative`.

In non-symlinked directories, Ruby will de-duplicate these duplicate requires automatically and the files will only get loaded once.
In the symlinked case, Ruby's de-duplication won't work because files loaded via `require_relative` are tracked by their canonical path, while files loaded via `require` are tracked by their requested path (which includes the symlink name).

This fix ensures that the files loaded via `require` will be requested using their canonical path, which should be identical to the path Ruby uses for files loaded via `require_relative`.
newrelic/centurion