Bumps twemoji files to 17.0.2.

Fixes #59

Bot steps:

• Update package.json and package-lock.json with new Twemoji version.
• Update images.
• Update TWEMOJI_VERSION constant in namespace.php file.

Human steps:

• Apply a minor version bump to the plugin, ie 0.1.0.
  • Run npm --no-git-tag-version version minor
  • Version number in PHP header
  • Stable version in readme.txt header
  • PLUGIN_VERSION constant in main namespace file.
  • Update changelog file.
• Increase WP minimum required version if applicable.