Add base64 dependency to gemspec

[wozozo]

This pull request includes a minor change to the payjp.gemspec file, which adds a new dependency to the project.

• Added base64 as a new dependency in the payjp.gemspec file.

fix #38

[Copilot]

PR Overview

This pull request adds a new dependency to the gemspec file by including the 'base64' library.

• Added 'base64' dependency to payjp.gemspec
• Minor update to the gemspec to address issue #38

Reviewed Changes

File	Description
payjp.gemspec	Adds the 'base64' dependency to gemspec

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

Comments suppressed due to low confidence (1)

payjp.gemspec:16

• The 'base64' library is part of Ruby's standard library, so adding it as an external dependency might be unnecessary unless there's a specific reason. Consider removing the dependency declaration if it's not required.

  s.add_dependency('base64')