refactor: replace string initialization with String.new for clarity

[wozozo]

This pull request includes a change to the lib/payjp/util.rb file to improve the url_encode method. The change replaces the initialization of a temporary string variable from an empty string to a new String object for better clarity and potential performance benefits.

• lib/payjp/util.rb: Modified the url_encode method to initialize the tmp variable using String.new instead of an empty string.

fix #39

[Copilot]

PR Overview

This PR refactors the initialization of the temporary variable in the url_encode method for clarity and potential performance benefits.

• Replaces the empty string initialization with String.new in the url_encode method.
• Addresses issue #39.

Reviewed Changes

File	Description
lib/payjp/util.rb	Changed the tmp variable initialization from an empty string to String.new for clarity.

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.