message: chore: Fix links in 6.18.1 changelog entry
diff: ## 6.18.1
  -- fix(ember): use _backburner if it exists (#4603)
  -- feat(gatsby): Upgrade Sentry Webpack Plugin to 1.18.8 (#4636)
  -- feat(nextjs): Upgrade Sentry Webpack Plugin to 1.18.8 (#4643)
  -- fix(nextjs): webpack as optional peer-dependency (#4634)
  +- fix(ember): use _backburner if it exists ([#4603](https://github.com/getsentry/sentry-javascript/pull/4603))
  +- feat(gatsby): Upgrade Sentry Webpack Plugin to 1.18.8 ([#4636](https://github.com/getsentry/sentry-javascript/pull/4636))
  +- feat(nextjs): Upgrade Sentry Webpack Plugin to 1.18.8 ([#4643](https://github.com/getsentry/sentry-javascript/pull/4643))
  +- fix(nextjs): webpack as optional peer-dependency ([#4634](https://github.com/getsentry/sentry-javascript/pull/4634))
  Work in this release contributed by @belgattitude, @pbernery, and @kylemh. Thank you for your contributions!
  